DISSECTION OF THE PELVIS AND PERINEUM

DISSECTION OF THE PELVIS AND PERINEUM

TABLE OF CONTENTS

1. OSTEOLOGY OF THE PELVIS

2. THURSDAY, JANUARY 21 –ANAL TRIANGLE

3. TUESDAY, JANUARY 26 – MALE EXTERNAL GENITALIA AND PERINEUM

4. TUESDAY, JANUARY 26 – FEMALE EXTERNAL GENITALIA AND PERINEUM

5. WEDNESDAY, JANUARY 27 – MALE PELVIC CAVITY AND PELVIC DIAPHRAGM

6. WEDNESDAY, JANUARY 27 – FEMALE PELVIC CAVITY AND PELVIC DIAPHRAGM

7. FOCUS QUESTIONS AND ANSWERS

Upon completion of these dissection sequences, the student will be able to:

1. Trace the continuity of the abdominal peritoneum with that of the pelvic cavity, and identify the peritoneal pouches of the pelvic floor in both sexes.

2. Identify the superficial features of the external genitalia.

3. Recognize the features of the rectum that differentiate it from the colon.

4. Describe the point at which the anal canal begins.

5. Describe the internal features of the anal canal, and determine the point at which its lining changes from cutaneous to mucosal.

6. Recall the lymph node groups that drain the anal canal.

7. Organize blood and nerve supply to the anal canal.

8. Recognize the urinary bladder in either its expanded or contracted position, and determine the extent of its peritoneal covering.

9. Identify the internal orifices of the bladder and differentiate the trigone region from the rest of the bladder lining.

10. Describe the relationships of the bladder to other pelvic organs in both sexes.

11. Describe the normal position and relationships of all organs of the reproductive tracts in both sexes and the role of each in reproductive processes.

12. Describe the broad ligament and differentiate its parts.

13. Identify the ovary and discuss the functional significance of its ligaments.

14. Demonstrate the uterine tube and its subdivisions.

15. Identify the uterus and its subdivisions and demonstrate the continuity of its lumen with that of the uterine tubes and the vagina.

16. Differentiate between the internal and external os of the cervix.

17. Identify the vagina, and note the angle formed at its junction with the uterus.

18. Trace the entire course of the ductus deferens and identify its ampulla; note its relationship to the ureter.

19. Identify the seminal vesicle and demonstrate the formation and course of the ejaculatory duct.

20. Identify the prostate gland and describe the special features of the prostatic urethral wall.

21. Describe the formation of the two sciatic foramina. List the muscles, nerves, and vessels which pass through each.

22. Demonstrate the origins of the piriformis and obturator internus muscles and describe two specializations of the obturator fascia.

23. Identify the pelvic diaphragm and differentiate its components.

24. Trace the branching pattern of the internal iliac vessels in each sex, identifying branches by their relationships to pelvic organs or wall structures.

25. Demonstrate the formation of the sacral plexus, its relationship to the piriformis muscle and gluteal vessels, and its pelvic splanchnic nerves.

26. Identify and describe the inferior hypogastric (pelvic) plexus and its connections to the superior hypogastric plexus via the hypogastric nerves.

27. Identify and describe the sacral sympathetic trunks and the sacral sympathetic nerves.

28. Trace the sympathetic and parasympathetic nerve supply to any pelvic organ, listing the location of the preganglionic cell body, the course of preganglionic fibers, the location of the postganglionic cell body, and the course of postganglionic fibers.

29. Trace the skeletal and ligamentous boundaries of the perineum, and define the anal and urogenital triangles.

30. Describe the position and boundaries of the ischioanal fossa.

31. Describe the structure, contents, and course of the pudendal canal.

32. Trace the branching pattern of the internal pudendal vessels and the pudendal nerve.

33. Differentiate between the internal and external anal sphincters in structure and function.

34. Differentiate between male and female urethrae.

35. Identify the components of the external genital organs and give the homologues in each of both sexes.

36. Describe structure and function of the erectile bodies.

37. Trace the nerve and blood supply to the external genital organs.

38. Trace the lymphatic drainage of the perineum.

The pelvis is the area of transition between the trunk and the lower limbs. The bony pelvis serves as the foundation for the pelvic region and provides strong support for the vertebral column upon the lower limbs. The pelvic cavity is continuous with the abdominal cavity, the transition occurring at the plane of the pelvic inlet (Figure 5.1). The pelvic cavity contains the rectum, the urinary bladder, and the internal genitalia. The perineum is the region of the trunk that is located between the thighs. The pelvic diaphragm separates the pelvic cavity from the perineum (Figure 5.1). The perineum contains the anal canal, the urethra, and the external genitalia (penis and scrotum in the male, vulva in the female).

This chapter begins with the dissection of the anal triangle. Following this dissection, the external genitalia and the perineum will be dissected. Each dissection team should partner with another dissection team that is working on a cadaver of the opposite sex.

Refer to an articulated bony pelvis. The pelvis (L. pelvis, basin) is formed by two hip bones (os coxae) joined posteriorly by the sacrum (Figure 5.2A). Each hip bone is formed by three fused bones: pubis, ischium, and ilium. The point of fusion of these three bones is the acetabulum. The coccyx is attached to the sacrum.

OSTEOLOGY OF THE PELVIS

On the hip bone, identify (Figure 5.2A,B):

Iliac fossa
Iliopubic eminence
Arcuate line
Pecten pubis
Superior pubic ramus
Pubic symphysis
Pubic arch
Ischiopubic ramus – formed by the ischial ramus and the inferior pubic ramus
Obturator foramen
Ischial tuberosity
Ischial spine

On the sacrum, identify:

Sacral promontory
Anterior sacral foramina

Identify the coccyx.

The hip bone and sacrum are connected by strong ligaments. On a model with pelvic ligaments, identify (Figure 5.2A,B):

· Sacrotuberous ligament

Sacrospinous ligament
Greater sciatic foramen
Lesser sciatic foramen

Note that the sacrotuberous ligament and sacrospinous ligament convert the greater and lesser sciatic notches into the greater and lesser sciatic foramina.

The sacroiliac articulation is a synovial joint between the auricular surfaces of the sacrum and the ilium. It is strengthened by an anterior sacroiliac ligament and a posterior sacroiliac ligament (Figure 5.2A,B). The articulation between the ilium and the L5 vertebra is strengthened by the iliolumbar ligament.

Identify the pubic arch. Note that the subpubic angle (angle of the pubic arch) is wider in females than males.

Identify the pelvic inlet (superior pelvic aperture). The bony rim of the pelvic inlet is called the pelvic brim. From anterior to posterior, identify the structures that form the pelvic brim:

Superior margin of the pubic symphysis
Posterior border of the pubic crest
Pecten pubis
Arcuate line of the ilium
Anterior border of the ala (wing) of the sacrum
Sacral promontory

Identify the pelvic outlet. The pelvic outlet is bounded on each side by:

Inferior margin of the pubic symphysis
Ischiopubic ramus
Ischial tuberosity
Sacrotuberous ligament
Tip of the coccyx

The pelvic inlet divides the pelvis into the greater (false) pelvis and the lesser (true) pelvis (Figure 5.1). The greater pelvis is situated superior to the pelvic brim and is bounded bilaterally by the ala of the ilium. The lesser pelvis is located inferior to the pelvic brim. The inferior boundary of the lesser pelvis is the pelvic diaphragm.

In the erect posture (anatomical position), the anterior superior iliac spines (ASIS) and the anterior aspect of the pubis are in the same vertical plane. In this position, the plane of the pelvic inlet forms an angle of approximately 55° to the horizontal (See Figure).

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THURSDAY, JANUARY 21 - DISSECTION OF THE ANAL TRIANGLE

Dissection Overview

The perineum is a diamond-shaped area between the thighs that is divided for descriptive purposes into two triangles (Figure 5.3). The anal triangle is the posterior part of the perineum and it contains the anal canal and anus. The urogenital triangle is the anterior part of the perineum and contains the urethra and the external genitalia. At the outset of dissection, it is important to understand that the pelvic diaphragm separates the pelvic cavity from the perineum (Figure 5.1).

The order of dissection will be as follows: Dissection of the anal triangle will begin with removal of skin covering the ischioanal fossa. The nerves and vessels of the ischioanal fossa will be dissected. The fat will be removed from the ischioanal fossa to reveal the inferior surface of the pelvic diaphragm.

Dissection Instructions

Skin and Superficial Fascia Removal

1. Place the cadaver in the supine position.

2. Stretch the thighs widely apart and brace them using the metal hardware available in the lab. Your instructor will demonstrate the use of this hardware. Usually only one student can work on the anal triangle at a time. The dissector should be positioned between the thighs with the cadaver pulled to the end of the dissection table.

3. Refer to Figures 20-4 and 20-5.

4. Make a transverse incision through the skin between the right (A) and left (B) ischial tuberosities. This incision should pass through the skin superficial to the perineal body (D).

5. Make a midline skin incision from the position of the perineal body (D) to the coccyx (E), encircling the anal orifice.

6. Detach the skin along a line between points A and E (also B and E) at the boundary between the perineum and the thigh. This line roughly corresponds in position to the inferior border of the gluteus maximus muscle and, deep to it, the sacrotuberous ligament.

Ischioanal Fossa

The ischioanal (ischiorectal) fossa is a wedge-shaped area on either side of the anus. The apex of the wedge is directed superiorly and the base is beneath the skin. The ischioanal fossa is filled with fat that helps accommodate the fetus during childbirth or the distended anal canal during the passage of feces. The ischioanal fat is part of the superficial fascia of this region. The goal of this dissection is to remove the fat and identify the nerves and vessels that pass through the ischioanal fossa. The following figures depict a male, but the dissection procedure is the same for a female.

1. Use blunt dissection to clean the external anal sphincter muscle (Figure 5.6x). To assist in cleaning the external anal sphincter muscle, a cylindrical object (to be provided by your instructor) may be placed into the anal canal. The external anal sphincter muscle has three parts (YOU DO NOT HAVE TO DISTINGUISH THESE – BUT DO KNOW HOW THE SPHINCTER IS ORGANIZED):

a. Subcutaneous – encircling the anus (not visible in dissection)

b. Superficial – anchoring the anus to the perineal body and coccyx

c. Deep – a circular band that is fused with the pelvic diaphragm

2. Lateral to the anus, insert closed scissors into the ischioanal fat to a depth of 3 cm. Open the scissors in the transverse direction to tear the fat (Figure 5.6x, incision on the left side of the figure).

3. Insert your finger into the incision and carefully move it back and forth (medial to lateral) to enlarge the opening.

4. Palpate the inferior rectal (anal) nerve and vessels (Figure 5.6x, right side of the figure). Preserve the branches of the inferior rectal nerve and vessels but use blunt dissection to remove the fat that surrounds them. Dry the area with towels if necessary.

5. Use blunt dissection to clean the inferior surface of the pelvic diaphragm (the medial boundary of the ischioanal fossa).

6. Use blunt dissection to clean the fascia of the obturator internus muscle (the lateral boundary of the ischioanal fossa).

7. Observe that the inferior rectal nerve and vessels penetrate the fascia of the obturator internus muscle to enter the ischioanal fossa.

8. Place gentle traction on the inferior rectal vessels and nerves and observe that a ridge is raised in the obturator internus fascia. The potential space deep to this ridge is called the pudendal canal. Carefully incise the obturator fascia along this ridge to open the pudendal canal.

9. Use a probe to elevate and clean the contents of the pudendal canal. The pudendal canal contains the pudendal nerve and the internal pudendal artery and vein.

10. Use a cadaveric pelvis to review the relationships between the greater and lesser sciatic foramina, the ischial spine, and the sacrotuberous and sacrospinous ligaments.

11. In the cadaver, locate and clean the inferior border of the gluteus maximus muscle.

12. Just medial to the pudendal nerve and internal pudendal vessels, gradually cut a notch through the fibers of the gluteus maximus muscle (Figure 15-3). Alternate between cutting and palpation until the sacrotuberous ligament can be felt.

13. Look for the pudendal nerve and internal pudendal artery where they pass anterior (deep) to the sacrotuberous ligament (Figure 15-3).

14. Anterior (deep) to the pudendal nerve and internal pudendal artery is the sacrospinous ligament.

Dissection Review

Review the boundaries of the true pelvis and the concept that the pelvic diaphragm separates the pelvic cavity from the perineum.
In the dissected specimen, review the inferior surface of the pelvic diaphragm and understand that this is the “roof” of the perineum.
Use the dissected specimen to review the lateral and medial walls of the ischioanal fossa.
Review the external anal sphincter muscle and its blood and nerve supply. Understand that the external anal sphincter muscle is skeletal muscle under voluntary control.

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TUESDAY, JANUARY 26 – MALE EXTERNAL GENITALIA AND PERINEUM

IF YOU HAVE A MALE CADAVER, YOU HAVE ALREADY DISSECTED THE SCROTUM AND TESTES. REVIEW THIS ANATOMY AND PROCEED WITH THE DISSECTION OF THE UROGENITAL TRIANGLE.

Male Urogenital Triangle

Dissection Overview

The order of dissection of the male urogenital triangle will be as follows: The skin will be removed from the urogenital triangle. The superficial perineal fascia will be removed and the contents of the superficial perineal pouch will be identified. The skin will be removed from the penis and its parts will be studied. The contents of the deep perineal pouch will be described, but not dissected.

Dissection Instructions

Skin Removal

Partner with a dissection team that has a female cadaver for the following dissection. You are expected to know the anatomical details for both sexes.
Place the cadaver in the supine position. Stretch the thighs widely apart and brace them using the metal hardware available in the lab. Your instructor will demonstrate the use of this hardware. Usually, only one student can work on the urogenital triangle at a time. The dissector should be positioned between the thighs with the cadaver pulled to the end of the dissection table.
Make a skin incision that encircles the proximal end of the penis (Figure 5.10, blue dashed lines). The skin is very thin.
Make a midline skin incision posterior to the proximal end of the penis that splits the scrotum along the scrotal septum. Carry the cut posteriorly to the previous transverse cut anterior to the anus.
Make an incision in the midline superior to the penis. Stop where the skin of the abdomen was reflected previously.
Reflect the skin flaps from medial to lateral.
If the cadaver has a large amount of fat in the superficial fascia of the medial thighs, remove a portion of the superficial fascia starting at the ischiopubic ramus and extending down the medial thigh about 7 cm. Stay superficial to the deep fascia when removing the superficial fascia.
Identify the posterior scrotal nerves and arteries, which enter the urogenital triangle by passing lateral to the external anal sphincter muscle. The posterior scrotal nerves and arteries supply the posterior part of the scrotum. The posterior scrotal nerves and arteries are terminal branches of the perineal nerve and artery, which can be traced from the pudendal nerve and internal pudendal artery, respectively.

Superficial Perineal Pouch

The superficial perineal fascia has a superficial fatty layer and a deep membranous layer. The superficial fatty layer is continuous with the superficial fatty layer of the lower abdominal wall, ischioanal fossa, and thigh. The deep membranous layer of the superficial perineal fascia (Colles' fascia) is continuous with the membranous layer of the superficial fascia of the anterior abdominal wall (Scarpa's fascia) and the dartos fascia of the penis and scrotum (Figure 5.11A). The membranous layer of the superficial perineal fascia is attached to the ischiopubic ramus as far posteriorly as the ischial tuberosity and to the posterior edge of the inferior fascia of the urogenital diaphragm (perineal membrane). The membranous layer of the superficial perineal fascia forms the superficial boundary of the superficial perineal pouch (space).

IN THE CLINIC: Superficial Perineal Pouch

If the urethra is injured in the perineum, urine may escape into the superficial perineal pouch. The urine may spread into the scrotum and penis, and upward into the lower abdominal wall between the membranous layer of the abdominal superficial fascia (Scarpa's fascia) and the aponeurosis of the external oblique muscle (Figure 5.11B). The urine does not enter the thigh because the membranous layer of the superficial fascia attaches to the fascia lata, ischiopubic ramus, and posterior edge of the perineal membrane.

1. The contents of the superficial perineal pouch in the male are three paired muscles (superficial transverse perineal, bulbospongiosus, and ischiocavernosus), the crura of the penis, and the bulb of the penis (Figure 5.12A,B). The superficial perineal pouch also contains the branches of the perineal arteries, veins, and nerves that supply these structures.

2. It is not necessary to identify the membranous layer of the superficial perineal fascia (Colles’ fascia) to complete the dissection. Use a probe to dissect through the superficial perineal fascia in the midline.

3. Use blunt dissection to find the bulbospongiosus muscle in the midline of the urogenital triangle (Figure 5.12A). The bulbospongiosus muscle covers the superficial surface of the bulb of the penis. The posterior attachments of the bulbospongiosus muscle are the bulbospongiosus muscle of the opposite side (in a midline raphe) and the perineal body. The anterior attachment of the bulbospongiosus muscle is the corpus cavernosum penis. The bulbospongiosus muscle compresses the bulb of the penis to expel urine or semen.

4. Lateral to the bulbospongiosus muscle, use a probe to clean the surface of the ischiocavernosus muscle (Figure 5.12A). The ischiocavernosus muscle covers the superficial surface of the crus of the penis. The proximal attachment of the ischiocavernosus muscle is the ischial tuberosity and the ischiopubic ramus. The distal attachment of the ischiocavernosus muscle is the crus of the penis. The ischiocavernosus muscle forces blood from the crus of the penis into the distal part of the corpus cavernosum penis.

5. Using blunt dissection, attempt to find the superficial transverse perineal muscle at the posterior border of the urogenital triangle (Figure 5.12A). The superficial transverse perineal muscle may be delicate and difficult to find; limit the time spent looking for it. The lateral attachments of the superficial transverse perineal muscle are the ischial tuberosity and the ischiopubic ramus. The medial attachment of the superficial transverse perineal muscle is the perineal body. The perineal body is a fibromuscular mass located anterior to the anal canal and posterior to the perineal membrane that serves as an attachment for several muscles. The superficial transverse perineal muscle helps to support the perineal body.

6. Use a probe to dissect between the three muscles of the superficial perineal pouch until a small triangular opening is created (Figure 5.12A). The membrane that becomes visible through this opening is the inferior fascia of the urogential diaphragm (perineal membrane). The perineal membrane is the deep boundary of the superficial perineal pouch and the bulb of the penis and crura are attached to it.

7. Use a scalpel to divide the bulbospongiosus muscles along their midline raphe. On the right side of the cadaver only, remove the bulbospongiosus muscle. NOTE: If your muscles are better on the right side, remove the muscles from the left side.

8. Identify the bulb of the penis on the side in which the bulbospongiosus muscle has been removed (Figure 5.12B). The bulb of the penis is continuous with the corpus spongiosum penis and contains a portion of the spongy urethra.

9. On the right side of the cadaver only, use blunt dissection to remove the ischiocavernosus muscle from the crus of the penis (Figure 5.12B) (L. crus, a leg-like part; pl. crura). The crus of the penis is the proximal part of the corpus cavernosum penis.

Penis

In the anatomical position, the penis is erect. The surface of the penis that is closest to the anterior abdominal wall is the dorsal surface of the penis.

Study a drawing of a transverse section of the penis (L. penis, tail) (Figure 5.13). The superficial fascia of the penis (dartos fascia) has no fat, and contains the superficial dorsal vein of the penis. The deep fascia of the penis (Buck's fascia) is an investing fascia. Contained within the deep fascia of the penis are the corpus spongiosum, corpus cavernosum (paired), deep dorsal vein of the penis (unpaired), dorsal artery of the penis (paired), and dorsal nerve of the penis (paired).

1. Identify the parts of the penis:

a. Root (bulb and crura)

b. Body (shaft)

c. Glans penis

d. Corona of the glans

e. Prepuce

f. Frenulum

g. External urethral orifice

2. Use a scalpel to make a midline skin incision down the ventral surface of the penis. Remove the skin from the body of the penis, detaching it around the corona of the glans. Do not skin the glans.

3. Use a probe to dissect the superficial dorsal vein of the penis. The superficial dorsal vein of the penis drains into the superficial external pudendal vein of the inguinal region.

On the dorsum of the penis, use a probe to dissect through the deep fascia of the penis and identify (Figure 5.14):

Deep dorsal vein of the penis – a single vein in the midline. Most of the blood from the penis drains through the deep dorsal vein into the prostatic venous plexus.
Dorsal artery of the penis (2) – one artery on each side of the deep dorsal vein. The dorsal artery of the penis is a terminal branch of the internal pudendal artery.

Dorsal nerve of the penis (2) – one nerve on each side of the midline, lateral to the deep dorsal artery. The dorsal nerve of the penis is a branch of the pudendal nerve.

Use a probe to trace the vessels and nerves of the penis proximally. Use an illustration to study the course of the pudendal nerve and the internal pudendal artery (Figure 5.14). Observe that the dorsal artery and nerve of the penis course deep to the perineal membrane before they emerge onto the dorsum of the penis. The deep dorsal vein passes between the inferior pubic ligament and the anterior edge of the perineal membrane to enter the pelvis. Note that the deep dorsal vein does not accompany the deep dorsal artery and dorsal nerve proximal to the body of the penis.

Spongy Urethra

The male urethra consists of three portions: prostatic urethra, membranous urethra, and spongy urethra (Figure 5.15). The spongy urethra is the portion that is located within the corpus spongiosum penis. The next objective is to longitudinally open the spongy urethra.

Examine the external urethral orifice at the tip of the glans penis. Push a probe into the external urethral orifice, and then use a scalpel to cut down to the probe from both the dorsal and ventral surfaces of the penis. Cut in the median plane of the penis (it may not be a straight line).

Advance the probe proximally, and continue to divide the penis. Dorsal to the probe, the cut should pass between the corpora cavernosa and may split the deep dorsal vein longitudinally. Stop inferior to the pubic symphysis where the two corpora cavernosa separate. Ventral to the probe the cut should divide the corpus spongiosum into equal halves. Stop at the bulb of the penis.
In the bulb of the penis, the urethra bends at a sharp angle and passes through the perineal membrane (Figure 5.15). Carefully complete the cut through the bulb posterior to the urethra but do not cut through the perineal membrane.
Note that the glans penis (L. glans, acorn) is the distal expansion of the corpus spongiosum and that it caps the two corpora cavernosa penis. The spongy urethra terminates by passing through the glans.
Examine the interior of the spongy urethra. Identify the navicular fossa, a widening of the urethra in the glans penis.
The openings of the ducts of the bulbourethral glands are in the proximal part of the spongy urethra, but may be too small to see.
On the right side of the penis, make a transverse cut through the body of the penis about midway down its length.
On the cut surface of the transverse section of the penis, study the relationship of the corpus cavernosum penis and corpus spongiosum penis. Identify (Figure 5.13):

Tunica albuginea of the corpus cavernosum penis
Tunica albuginea of the corpus spongiosum penis
Septum penis

Study the erectile tissue within the corpus spongiosum penis. Observe that the corpus spongiosum penis surrounds the spongy urethra.
Study the erectile tissue within the corpus cavernosum penis (Figure 5.13). Identify the deep artery of the penis near the center of the erectile tissue. Review the origin of the deep artery of the penis from the internal pudendal artery.

Deep Perineal Pouch

The deep perineal pouch (space) will not be dissected. The deep perineal pouch lies superior (deep) to the perineal membrane (Figure 5.15). The contents of the deep perineal pouch in the male (Figure 5.16) include the membranous urethra, external urethral sphincter muscle, bulbourethral glands, the dorsal artery of the penis (a branch of the internal pudendal artery), and the dorsal nerve of the penis (a branch of the pudendal nerve).

Use an illustration to study the following:

Membranous urethra – extends from the perineal membrane to the prostate gland (Figure 5.15). This is the shortest (about 1 cm), thinnest, narrowest, and least distensible part of the urethra.
External urethral sphincter (sphincter urethrae) muscle – a voluntary muscle that surrounds the membranous urethra (Figure 5.16). When the external urethral sphincter muscle contracts, it compresses the membranous urethra and stops the flow of urine.
Deep transverse perineal muscle – has a lateral attachment to the ischial tuberosity and the ischiopubic ramus and a medial attachment to the perineal body (Figure 5.16). Its fiber direction and function are identical to those of the superficial transverse perineal muscle, which is a content of the superficial perineal pouch.

The bulbourethral glands are located in the deep perineal pouch. The duct of the bulbourethral gland passes through the perineal membrane and drains into the proximal portion of the spongy urethra.
The deep perineal pouch contains branches of the pudendal nerve and internal pudendal artery. These structures supply the external urethral sphincter muscle, the deep transverse perineal muscle, and the penis (Figure 5.16).
Collectively, the muscles within the deep perineal pouch plus the perineal membrane are known as the urogenital diaphragm. This older anatomical nomenclature is still in clinical use.

Dissection Review

Return the muscles of the urogenital triangle to their correct anatomical positions.
Review the contents of the male superficial perineal pouch. Visit a dissection table with a female cadaver and view the contents of the superficial perineal pouch.
Use an illustration to review the course of the internal pudendal artery from its origin in the pelvis to the dorsum of the penis.
Use an illustration to review the course and branches of the pudendal nerve.
Study an illustration showing the course of the deep dorsal vein of the penis into the pelvis to join the prostatic venous plexus.
Draw a cross section of the penis showing the erectile bodies, superficial fascia, deep fascia, vessels, and nerves.
Obtain an illustration that shows the entire male urethra and review its parts.

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TUESDAY, JANUARY 26 – FEMALE EXTERNAL GENITALIA AND PERINEUM

Female External Genitalia and Perineum

Labium Majus

Dissection Overview

In the female, the round ligament of the uterus passes through the superficial inguinal ring and descends into the fat that forms the labium majus. The layers of the scrotum that are identified in the male are not found in the labium majus.

Dissection Instructions

At the superficial inguinal ring, use blunt dissection to demonstrate that the round ligament of the uterus emerges from the superficial inguinal ring and spreads out into the fatty tissue of the labium majus. The round ligament is a delicate structure that can be demonstrated for only 1 to 2 cm distal to the superficial inguinal ring.

IN THE CLINIC: Lymphatic Drainage of the Labium Majus

Lymphatics from the labium majus drain to the superficial inguinal lymph nodes. Inflammation of the labium majus may cause tender, enlarged superficial inguinal lymph nodes.

Dissection Review

Review the course of the round ligament from the abdominal wall to the labium majus.
Review the embryology of the ovary and testis and compare the role of the gubernaculum in each case. Review the adult structures that are formed from the gubernaculum in both sexes.
Complete the dissection review that follows the dissection of the spermatic cord and testis

Female Urogenital Triangle

Dissection Overview

The order of dissection of the female urogenital triangle will be as follows: The external genitalia will be examined. The superficial perineal fascia will be removed and the contents of the superficial perineal pouch will be identified. The contents of the deep perineal pouch will be described, but not dissected.

Dissection Instructions

External Genitalia

Partner with a dissection team that has a male cadaver for the following dissection. You are expected to know the anatomical details for both sexes.
Place the cadaver in the supine position. Stretch the thighs widely apart and brace them using the hardware available in the lab (your lab instructor will show you how to use the hardware). Usually, only one student can work on the urogenital triangle at a time. The dissector should be positioned between the thighs with the cadaver pulled to the end of the dissection table.
Examine the vulva (female external genitalia) (Figure 5.25). Identify the following structures:

Mons pubis
Anterior labial commissure
Labium majus
Clitoris

Prepuce
Glans
Frenulum of clitoris

Labium minus
Vestibule of the vagina – the area between the labia minora
External urethral orifice
Vaginal orifice
Openings of the paraurethral ducts – on each side of the external urethral orifice
Frenulum of labia minora
Posterior labial commissure

Superficial Perineal Pouch and Clitoris

The superficial perineal fascia has a superficial fatty layer and a deep membranous layer. In the female, the superficial fatty layer provides the shape of the labium majus and is continuous with the fat of the lower abdominal wall, ischioanal fossa, and thigh. The membranous layer of the superficial perineal fascia (Colles' fascia) is attached to the ischiopubic ramus as far posteriorly as the ischial tuberosity, and to the posterior edge of the inferior fascia of the urogenital diaphragm (perineal membrane) (Figure 5.27). The membranous layer of the superficial perineal fascia forms the superficial boundary of the superficial perineal pouch (space).

Dissection of the superficial pouch of the female urogenital triangle

1. Make an incision in the skin fold of the groin, that is, where the lateral aspects of the labia majora (hair-covered outer folds of the female external genitalia) meet the thigh.

2. From the incision and using blunt dissection as much as possible, roll the cut edge of the labial skin anteriorly and medially. This will preserve the rest of the external genitalia – labia minora, clitoris, vaginal opening etc but allow you to study the structures of the superficial pouch

3. Bulbospongiosus muscles

The bulbospongiosus muscles (Figure 5.28A) are lateral to the labia minora and encircle the vaginal opening. Locate the vaginal opening. Using the index finger and thumb, insert one digit into the vaginal opening and palpate between the thumb and index finger the bulb of the vestibule covered superficially by the bulbospongiosus muscles. It is not a very robust structure.

Expose the bulbospongiosus muscles by gently removing the fat and fascia, being careful to preserve the posterior labial nerves and arteries. Other small branches of the perineal nerve and artery supply the muscles of the urogenital triangle. The perineal nerve and artery are branches of the pudendal nerve and internal pudendal artery, respectively.

4. Ischiocavernosus muscles

The ischiocavernosus muscles (Figure 5.28A) cover the superficial surface of the crura of the clitoris (L. crus, a leg-like part; pl. crura) (Figure 5.28B). The crus of the clitoris is the proximal part of the corpus cavernosum clitoris. The two corpora cavernosa form the body of the clitoris.

The proximal attachments of the ischiocavernosus muscle are the ischial tuberosity and ischiopubic ramus. The distal attachment of the ischiocavernosus muscle is to the crus of the clitoris. Locate the clitoris and palpate the glans and the body of the clitoris. Realize that the crus of the clitoris is continuous with the corpus cavernosum clitoris and the two corpora cavernosa form the body of the clitoris.

To expose the ischiocavernosus muscle, gently, with blunt dissection, remove the fascia and fat along the ischiopubic ramus. Most times you will encounter a thick shiny dense fascia covering the ischiocavernosus muscle. When you remove this layer, the ischiocavernosus muscle fibers will be seen.

5. Perineal membrane and superficial transverse perineal muscle

Clean the fat and fascia between the bulbospongiosus and ischiocavernosus muscles to expose the triangular inferior surface of the UG diaphragm, the inferior fascia of the urogenital diaphragm (perineal membrane). The base of the triangle from the perineal body (Figure 5.28A) (the median attachment of the bulbospongiosus muscles and superficial transverse perineal muscles) to the ischial tuberosity is delineated by the superficial transverse perineal muscle (Figure 5.28A). This is a delicate muscle and may be hard to dissect. The lateral attachment of the superficial transverse perineal muscle is the ischial tuberosity and the ischiopubic ramus. The medial attachment of the superficial transverse perineal muscle is the perineal body. The perineal body is a fibromuscular mass located between the anal canal and the posterior edge of the perineal membrane that serves as an attachment for several muscles. The superficial transverse perineal muscle helps to support the perineal body.

Use a probe to dissect between the three muscles of the superficial perineal pouch until a small triangular opening is created. The membrane that becomes visible through this opening is the perineal membrane (Figure 5.28A). The perineal membrane is the deep boundary of the superficial perineal pouch, and the bulb of the vestibule and crura are attached to it.

6. On one side of the cadaver only, reflect the bulbospongiosus muscle and ischiocavernosus muscle to demonstrate the erectile tissues, bulb of the vestibule (Figure 5.28B) and crus of the clitoris, respectively. Anteriorly, the bulbs of the two sides are joined at the commissure of the bulbs and the commissure is continuous with the glans of the clitoris. Do not attempt to find the commissure of the bulbs.

If possible, look for the greater vestibular gland (Figure 5.28B) immediately posterior to the bulb of the vestibule.

7. DO NOT DISSECT THE DEEP PERINEAL POUCH.

Deep Perineal Pouch

The deep perineal pouch (space) will not be dissected. The deep perineal pouch lies superior (deep) to the perineal membrane (Figure 5.27). The contents of the deep perineal pouch in the female (Figure 5.29) include the urethra, a portion of the vagina, the external urethral sphincter muscle, the dorsal artery of the clitoris (a branch of the internal pudendal artery), and the dorsal nerve of the clitoris (a branch of the pudendal nerve).

Use an illustration to study the following:

Urethra – extends from the internal urethral orifice in the urinary bladder to the external urethral orifice in the vestibule of the vagina (about 4 cm).
External urethral sphincter (sphincter urethrae) muscle – a voluntary muscle that surrounds the urethra. When the external urethral sphincter muscle contracts, it compresses the urethra and stops the flow of urine.
Deep transverse perineal muscle – has a lateral attachment to the ischial tuberosity and the ischiopubic ramus and a medial attachment to the perineal body. Its fiber direction and function are identical to those of the superficial transverse perineal muscle (which is a content of the superficial perineal pouch).

Other contents of the deep perineal pouch include branches of the internal pudendal artery and branches of the pudendal nerve that supply the external urethral sphincter muscle, the deep transverse perineal muscle, and the clitoris (Figure 5.29).

Collectively, the muscles within the deep perineal pouch plus the perineal membrane are known as the urogenital diaphragm. This older anatomical nomenclature is still in clinical use.

IN THE CLINIC: Obstetric Considerations

As the head of the baby passes through the vagina during childbirth, the anus and the levator ani muscle are forced posteriorly toward the sacrum and coccyx. The urethra is forced anteriorly toward the pubic symphysis. Perineal lacerations during childbirth are common, and it may be necessary to surgically widen the vaginal orifice (episiotomy). If the perineal body is lacerated, it must be repaired to prevent weakness of the pelvic floor, which could result in prolapse of the urinary bladder, uterus, or rectum.

To alleviate the pain of childbirth, a pudendal nerve block is performed by injecting a local anesthetic around the pudendal nerve near the ischial spine. To perform the injection, the ischial spine is palpated through the vagina, and the needle is directed toward the ischial spine.

Dissection Review

Replace the muscles of the urogenital triangle in their correct anatomical positions.
Review the contents of the female superficial perineal pouch. Visit a dissection table with a male cadaver and view the contents of the superficial perineal pouch.
Use an illustration to review the course of the internal pudendal artery from its origin in the pelvis.
Use an illustration to review the course and branches of the pudendal nerve.
Review an illustration showing the urethra and note its course from the urinary bladder to the perineum.

RETURN TO TABLE OF CONTENTS

WEDNESDAY, JANUARY 27 – THE MALE PELVIC CAVITY AND THE PELVIC DIAPHRAGM

Dissection Overview

The male pelvic cavity contains the urinary bladder anteriorly, male internal genitalia, and the rectum posteriorly (Figure 5.17). The order of dissection will be as follows: The peritoneum will be studied in the male pelvic cavity. The pelvis will be sectioned in the midline and the cut surface of the sectioned pelvis will be studied. The ductus deferens will be traced from the anterior abdominal wall to the region between the urinary bladder and rectum. The seminal vesicles and prostate gland will be studied.

Dissection Instructions

Peritoneum

Using Figure 5.17 as a reference, examine the peritoneum in the male pelvis. Note that the peritoneum:

(1, 2) Passes from the anterior abdominal wall superior to the pubis
(3) Covers the superior surface of the urinary bladder
(4) Passes inferiorly along the posterior surface of the urinary bladder
(5) Has a close relationship to the superior ends of the seminal vesicles
(6) Passes inferiorly between the urinary bladder and the rectum to form the rectovesical pouch
(7) Contacts the anterior surface and sides of the rectum
(8) Forms the sigmoid mesocolon beginning at the level of the third sacral vertebra

Laterally, a paravesical fossa is apparent on each side of the urinary bladder. Further posteriorly, a pararectal fossa is apparent on each side of the rectum.

IN THE CLINIC: Pelvic Peritoneum

As the urinary bladder fills, the peritoneal reflection is elevated above the level of the pubis and is raised from the anterior abdominal wall. A filled urinary bladder can be approached with a needle just superior to the pubis without entering the peritoneal cavity.

Section of the Pelvis

The pelvis will be divided in the midline (Refer to Figure 5.40 – the figure demonstrates mobilization of only the right lower limb. The left lower limb will be mobilized in the same manner). First, the pelvic viscera and the soft tissues of the perineum will be cut in the midline with a scalpel. The pubic symphysis and vertebral column (up to the L3/L4 intervertebral disc) will be cut in the midline with a saw. Subsequently, the body will be transected at vertebral level L3/L4 to mobilize the lower limbs.

Both halves of the pelvis will be used to dissect the pelvic viscera, pelvic vasculature, and nerves of the pelvis. One half of the pelvis will be used to demonstrate the muscles of the pelvic diaphragm.

Begin this dissection with a new scalpel blade.
In the pelvic cavity make a midline cut, beginning posterior to the pubic symphysis. Carry this midline cut through the superior surface of the urinary bladder. Open the bladder and sponge the interior, if necessary.
Identify the internal urethral orifice and insert a probe. Use the probe as a guide and continue the midline cut inferior to the urinary bladder, dividing the urethra. Divide the prostate gland.
Extend the midline cut in the posterior direction. Cut through the anterior and posterior walls of the rectum and the distal part of the sigmoid colon. Sponge them clean.
In the perineum, insert the scalpel blade inferior to the pubic symphysis with the cutting edge directed inferiorly. Cut between the halves of the bulb of the penis (sectioned earlier). Make a cut in the midline from the pubic symphysis to the coccyx passing through the perineal membrane, perineal body, and anal canal.
Use a saw to make two cuts in the midline:

Pubic symphysis – Cut through the pubic symphysis from anterior to posterior.
Sacrum – Turn the cadaver to the prone position. Cut through the sacrum from posterior to anterior. Do not allow the saw to pass between the soft tissue structures that were cut with the scalpel. Spread the opening and extend the midline cut as far superiorly as the body of the third lumbar vertebra.

Return the cadaver to the supine position. Cut the right renal arteries and veins (do not cut the ureter) and place the right kidney in the pelvic cavity to protect the ureter from the subsequent transverse cut. Repeat for the left kidney.
To mobilize the lower limbs, use a scalpel to make a transverse cut through the soft tissues at vertebral level L3/L4.
In the transverse plane, use the saw to cut horizontally through the intervertebral disc between L3 and L4. Now, the lower limbs can be removed.
Clean the rectum and anal canal.

Male Internal Genitalia

Study the cut surface of the sectioned specimen. Use an illustration to guide you.

1. Identify the perineal membrane. It is located deep to the bulb of the penis and can be identified as a thin line at the deep edge of the bulb (Figure 5.15). Superior (deep) to the perineal membrane, the external urethral sphincter muscle surrounds the membranous urethra. The external urethral sphincter muscle may be difficult to see in the sectioned specimen.

2. On the sectioned pelvis, identify the three parts of the urethra: prostatic urethra, membranous urethra, and spongy urethra (Figure 5.15).

3. Examine the interior of the prostatic urethra. The prostatic urethra is about 3 cm in length and is the part that passes through the prostate. On the posterior wall of the prostatic urethra, identify if you can (these structures are really small and may not be visible if your cuts are off the mark) (Figure 5.18):

Urethral crest – a longitudinal ridge

Seminal colliculus – an enlargement of the urethral crest

Prostatic sinus – the groove on either side of the seminal colliculus

Prostatic utricle – a small opening on the midline of the seminal colliculus

Opening of the ejaculatory duct – one on either side of the prostatic utricle

4. Find the ductus deferens where it enters the deep inguinal ring lateral to the inferior epigastric vessels. Use a probe to break through the peritoneum at the deep inguinal ring. Use blunt dissection to peel the peritoneum off the lateral wall of the pelvis. Strip the peritoneum from lateral to medial, stopping where it comes in contact with the rectum and urinary bladder. Detach the peritoneum and place it in the tissue container.

5. Use blunt dissection to trace the ductus deferens from the deep inguinal ring toward the midline. Observe that the ductus deferens passes superior and then medial to the branches of the internal iliac artery. Note that the ductus deferens crosses superior to the ureter.

6. Trace the ductus deferens into the rectovesical septum, which is the endopelvic fascia between the rectum and the urinary bladder. Observe that the ductus deferens is in contact with the fundus (posterior surface) of the urinary bladder.

7. Identify the ampulla of the ductus deferens, which is the enlarged portion just before its termination (Figure 5.19).

8. Identify the seminal vesicle. The seminal vesicle is located lateral to the ampulla of the ductus deferens in the rectovesical septum. Use blunt dissection to release the seminal vesicle from the rectovesical septum.

9. Close to the prostate, the duct of the seminal vesicle joins the ductus deferens to form the ejaculatory duct. The ejaculatory duct is delicate and easily torn where it enters the prostate. The ejaculatory duct empties into the prostatic urethra on the seminal colliculus.

10. Observe the prostate. The apex of the prostate is directed inferiorly and the base of the prostate is located superiorly against the neck of the urinary bladder. Use a textbook to study the lobes of the prostate.

Dissection Review

Review the position of the male pelvic viscera within the lesser pelvis. Visit a dissection table with a female cadaver and observe the position of the female pelvic viscera.
Review the peritoneum in the male pelvic cavity. Visit a dissection table with a female cadaver and compare differences in the male and female peritoneum (Figs. 5.17 and 5.30).
Trace the ductus deferens from the epididymis to the ejaculatory duct, recalling its relationships to vessels, nerves, the ureter, and the seminal vesicle.
Visit a dissection table with a female cadaver and trace the round ligament of the uterus from the labium majus to the uterus.

Compare the pelvic course of the ductus deferens with the pelvic course of the round ligament of the uterus.

Urinary Bladder, Rectum, and Anal Canal

Dissection Overview

The urinary bladder is a reservoir for urine. When empty, it is located within the pelvic cavity. When filled, it extends into the abdominal cavity. The urinary bladder is a subperitoneal organ that is surrounded by endopelvic fascia. Between the pubic symphysis and the urinary bladder there is a potential space called the retropubic space (prevesical space) (Figure 5.17). The retropubic space is filled with fat and loose connective tissue that accommodates the expansion of the urinary bladder. The puboprostatic ligament is a condensation of fascia that ties the prostate to the inner surface of the pubis. The puboprostatic ligament defines the inferior limit of the retropubic space (Figure 5.17). The lower one-third of the rectum is surrounded by endopelvic fascia. The middle and upper thirds of the rectum are partially covered by peritoneum (Figure 5.17).

The order of dissection will be as follows: The parts of the urinary bladder will be studied. The interior of the urinary bladder will be studied. The interior of the rectum and anal canal will be studied.

Dissection Instructions

Urinary Bladder

1. Identify the parts of the urinary bladder (Figure 5.20):

a. Apex – the pointed part directed toward the anterior abdominal wall. The apex of the urinary bladder can be identified by the attachment of the urachus.

b. Body – between the apex and fundus.

c. Fundus – the inferior part of the posterior wall, also called the base of the urinary bladder. In the male the fundus is related to the ductus deferens, seminal vesicles, and rectum.

d. Neck – where the urethra exits the urinary bladder. In the neck of the urinary bladder, the wall thickens to form the internal urethral sphincter, which is an involuntary muscle.

2. Identify the four surfaces of the urinary bladder (Figure 5.20):

a. Superior – covered by peritoneum

b. Posterior – covered by peritoneum on its superior part and by the endopelvic fascia of the rectovesical septum on its inferior part

c. Inferolateral (2) – covered by endopelvic fascia

3. Examine the wall of the urinary bladder and note its thickness. The wall of the urinary bladder consists of bundles of smooth muscle called the detrusor muscle (L. detrudere, to thrust out).

4. Identify the trigone on the inner surface of the fundus (Figure 5.18). The angles of the trigone are the internal urethral orifice and the two orifices of the ureters. The internal urethral orifice is located at the most inferior point in the urinary bladder.

5. Observe that the mucous membrane over the trigone is smooth. The mucous membrane lining the other parts of the urinary bladder lies in folds when the bladder is empty but will accommodate expansion.

6. Insert the tip of a probe into the orifice of the ureter and observe that the ureter passes through the muscular wall of the urinary bladder in an oblique direction. When the urinary bladder is full (distended), the pressure of the accumulated urine flattens the part of the ureter that is within the wall of the bladder and prevents reflux of urine into the ureter.

7. Find the ureter where it crosses the external iliac artery or the bifurcation of the common iliac artery. Use blunt dissection to follow the ureter to the fundus of the urinary bladder.

IN THE CLINIC: Kidney Stones

Kidney stones pass through the ureter to the urinary bladder and they may become lodged in the ureter. The point where the ureter passes through the wall of the urinary bladder is a relatively narrow passage. If a kidney stone becomes lodged, severe colicky pain results. The pain stops suddenly once the stone passes into the bladder.

Rectum and Anal Canal

1. The rectum begins at the level of the third sacral vertebra. Observe the sectioned pelvis and note that the rectum follows the curvature of the sacrum.

2. Identify the ampulla of the rectum (Figure 5.21). At the ampulla, the rectum bends approximately 80° posteriorly (anorectal flexure) and is continuous with the anal canal. Observe that the prostate and seminal vesicles are located close to the anterior wall of the rectum (Figure 5.17).

3. Examine the inner surface of the rectum. Note that the mucous membrane is smooth except for the presence of transverse rectal folds. There is usually one transverse rectal fold on the right side and two on the left side. The transverse rectal folds may be difficult to identify in some cadavers.

4. Observe that the anal canal is only 2.5 to 3.5 cm in length. The anal canal passes out of the pelvic cavity and enters the anal triangle of the perineum.

5. Examine the inner surface of the anal canal (Figure 5.21). The mucosal features of the anal canal may be difficult to identify in older individuals, but attempt to identify the following:

a. Anal columns – 5 to 10 longitudinal ridges of mucosa in the proximal part of the anal canal. The anal columns contain branches of the superior rectal artery and vein.

b. Anal valves – semilunar folds of mucosa that unite the distal ends of the anal columns. Between the anal valve and the wall of the anal canal is a small pocket called an anal sinus.

c. Pectinate line – the irregular line formed by all of the anal valves.

6. The anal sphincter muscles surround the anal canal. Identify the external anal sphincter muscle and the internal anal sphincter muscle in the sectioned specimen (Figure 5.21). The longitudinal muscle of the anal canal separates the two sphincter muscles. If you have difficulty identifying them, use a new scalpel blade to cut another section through the wall of the anal canal to improve the clarity of the dissection.

IN THE CLINIC: Rectal Examination

Digital rectal examination is part of the physical examination. The size and consistency of the prostate gland can be assessed by palpation through the anterior wall of the rectum.

IN THE CLINIC: Hemorrhoids

In the anal columns, the superior rectal veins of the hepatic portal system anastomose with middle and inferior rectal veins of the inferior vena caval system. An abnormal increase in blood pressure in the hepatic portal system causes engorgement of the veins contained in the anal columns, resulting in internal hemorrhoids. Internal hemorrhoids are covered by mucous membrane and are relatively insensitive to painful stimuli because the mucous membrane is innervated by autonomic nerves.

External hemorrhoids are enlargements of the tributaries of the inferior rectal veins. External hemorrhoids are covered by skin and are very sensitive to painful stimuli because they are innervated by somatic nerves (inferior rectal nerves).

Dissection Review

Use the dissected specimen to review the features of the urinary bladder, rectum, and anal canal.

2. Review the relationships of the seminal vesicles, ampulla of the ductus deferens, and ureters to the rectum and fundus of the urinary bladder.

Visit a dissection table with a female cadaver and review the relationships of the uterus, vagina, and ureters to the rectum and fundus of the urinary bladder.
Review the kidney, the abdominal course of the ureter, the pelvic course of the ureter, and the function of the urinary bladder as a storage organ.
Review the parts of the male urethra. Visit a dissection table with a female cadaver and review the female urethra.
Review all parts of the large intestine and recall its function in absorption of water and in compaction and elimination of fecal material.
Recall that the external anal sphincter muscle is composed of skeletal muscle and is under voluntary control, whereas the internal anal sphincter muscle is composed of smooth muscle and is involuntary.

Internal Iliac Artery and Sacral Plexus

Dissection Overview

Anterior to the sacroiliac articulation, the common iliac artery divides to form the external and internal iliac arteries (Figure 5.22). The external iliac artery distributes to the lower limb and the internal iliac artery distributes to the pelvis. The internal iliac artery has the most variable branching pattern of any artery, and it is worth noting at the outset of this dissection that you must use the distribution of the branches to identify them, not their pattern of branching.

The internal iliac artery commonly divides into an anterior division and a posterior division. Branches arising from the anterior division are mainly visceral (branches to the urinary bladder, internal genitalia, external genitalia, rectum, and gluteal region). Branches arising from the posterior division are parietal (branches to the pelvic walls and gluteal region).

The order of dissection will be as follows: The branches of the anterior division of the internal iliac artery will be identified. The branches of the posterior division of the internal iliac artery will be identified. The nerves of the sacral plexus will be dissected. Subsequently, the pelvic portion of the sympathetic trunk will be dissected.

Dissection Instructions

Blood Vessels

The internal iliac vein is typically plexiform. To clear the dissection field, remove all tributaries to the internal iliac vein.
Identify the common iliac artery and follow it distally until it bifurcates.
Identify the internal iliac artery. Use blunt dissection to follow the internal iliac artery into the pelvis.
Identify the branches of the anterior division of the internal iliac artery (Figure 5.22):

Umbilical artery – in the medial umbilical fold, find the medial umbilical ligament (the obliterated portion of the umbilical artery) and use blunt dissection to trace it posteriorly to the umbilical artery. Note that several superior vesical arteries arise from the inferior surface of the umbilical artery and descend to the superolateral part of the urinary bladder.
Obturator artery – passes through the obturator canal. Find the obturator artery where it enters the obturator canal in the lateral wall of the pelvis and follow the artery posteriorly to its origin. In about 20% of cases an aberrant obturator artery (a branch of the external iliac artery) crosses the pelvic brim and is at risk of injury during surgical repair of a femoral hernia.
Inferior vesical artery – courses toward the fundus of the urinary bladder to supply the bladder, seminal vesicle, and prostate. The inferior vesical artery is a named branch only in the male; in the female it is an unnamed branch of the vaginal artery.
Middle rectal artery – courses medially toward the rectum. It often arises in common with the inferior vesical artery, making positive identification difficult. Identify the middle rectal artery by tracing it to the rectum. The middle rectal artery, like the inferior vesical artery, sends branches to the seminal vesicle and prostate.
Internal pudendal artery – exits the pelvic cavity by passing through the greater sciatic foramen inferior to the piriformis muscle. The internal pudendal artery often arises from a common trunk with the inferior gluteal artery.
Inferior gluteal artery – usually passes out of the pelvic cavity between ventral rami S2 and S3. The inferior gluteal artery exits the pelvis by passing through the greater sciatic foramen inferior to the piriformis muscle. The inferior gluteal artery may share a common trunk with the internal pudendal artery, or less commonly, with the superior gluteal artery.

Identify the branches of the posterior division of the internal iliac artery (Figure 5.22):

Iliolumbar artery – passes posteriorly, then ascends between the lumbosacral trunk and the obturator nerve. It may arise from a common trunk with the lateral sacral artery.
Lateral sacral artery – gives rise to a superior branch and an inferior branch. Observe the inferior branch that passes anterior to the sacral ventral rami.
Superior gluteal artery – usually exits the pelvic cavity by passing between the lumbosacral trunk and the ventral ramus of S1.

Use an illustration to study the prostatic venous plexus, vesical venous plexus, and rectal venous plexus. All of these plexuses drain into the internal iliac vein.
On the dissected specimen, observe the deep dorsal vein of the penis just inferior to the pubic symphysis. Verify that the deep dorsal vein of the penis empties into the prostatic venous plexus.

Nerves

The somatic plexuses of the pelvic cavity are the sacral plexus and coccygeal plexus. These plexuses are located between the pelvic viscera and the lateral pelvic wall within the endopelvic fascia. These somatic nerve plexuses are formed by contributions from ventral rami of spinal nerves L4 to S4. The primary visceral nerve plexus of the pelvic cavity is the inferior hypogastric plexus. It is formed by contributions from the hypogastric nerves, sympathetic trunks, and pelvic splanchnic nerves.

1. Use your fingers to dissect the rectum from the anterior surface of the sacrum and coccyx.

Retract the rectum medially and identify the sacral plexus of nerves. The sacral plexus is closely related to the anterior surface of the piriformis muscle. Verify the following (Figure 5.23):

The lumbosacral trunk (ventral rami of L4 and L5) joins the sacral plexus.
The ventral rami of S2 and S3 emerge between the proximal attachments of the piriformis muscle.
The sciatic nerve is formed by the ventral rami of spinal nerves L4 through S3. The sciatic nerve exits the pelvis by passing through the greater sciatic foramen, usually inferior to the piriformis muscle.
The superior gluteal artery usually passes between the lumbosacral trunk and the ventral ramus of spinal nerve S1, and exits the pelvis by passing superior to the piriformis muscle.
The inferior gluteal artery usually passes between the ventral rami of spinal nerves S2 and S3. The inferior gluteal artery exits the pelvis by passing inferior to the piriformis muscle.
The pudendal nerve receives a contribution from the ventral rami of spinal nerves S2, S3, and S4. The pudendal nerve exits the pelvis by passing inferior to the piriformis muscle.

3. Identify the pelvic splanchnic nerves (nervi erigentes). Pelvic splanchnic nerves are branches of the ventral rami of spinal nerves S2 through S4 (Figure 5.23). Pelvic splanchnic nerves carry preganglionic parasympathetic axons for the innervation of pelvic organs and the distal gastrointestinal tract (from the left colic flexure through the anal canal).

The sacral portion of the sympathetic trunk is located on the anterior surface of the sacrum, medial to the ventral sacral foramina. Identify the following:

Sympathetic trunk – continues from the abdominal region into the pelvis. The sympathetic trunks of the two sides join in the midline near the level of the coccyx to form the ganglion impar.
Gray rami communicantes – connect the sympathetic ganglia to the sacral ventral rami. Each gray ramus communicans carries postganglionic sympathetic fibers to a ventral ramus for distribution to the lower extremity and perineum.
Sacral splanchnic nerves – arise from two or three of the sacral sympathetic ganglia and pass directly to the inferior hypogastric plexus. Sacral splanchnic nerves carry sympathetic fibers that distribute to the pelvic viscera.

IN THE CLINIC: Pelvic Nerve Plexuses

The pelvic splanchnic nerves (parasympathetic outflow of S2, S3, and S4) are closely related to the lateral aspects of the rectum. The inferior hypogastric plexus is located in the connective tissue lateral to the prostate. These autonomic nerve plexuses can be injured during surgery, causing loss of bladder control and erectile dysfunction.

Dissection Review

Review the abdominal aorta and its terminal branches.
Use the dissected specimen to review the branches of the internal iliac artery. Review the region supplied by each branch.
Visit a dissection table with a female cadaver and review the arteries that are unique to the female: uterine artery and vaginal artery. Note their relationship to the ureter.
Review the formation of the sacral plexus and the branches that were dissected in the pelvis.
Use the dissected specimen and an illustration to review the course of the pudendal nerve from the pelvic cavity to the urogenital triangle.

Pelvic Diaphragm

Dissection Overview

The pelvic diaphragm is the muscular floor of the pelvic cavity. The pelvic diaphragm is formed by the levator ani muscle and coccygeus muscle plus the fasciae covering their superior and inferior surfaces (Figure 5.24A,B). The pelvic diaphragm extends from the pubic symphysis to the coccyx. Laterally, the pelvic diaphragm is attached to the fascia covering the obturator internus muscle. The urethra and anal canal pass through midline openings in the pelvic diaphragm called the urogenital hiatus and anal hiatus, respectively.

Dissection Instructions

Perform the dissection of the pelvic diaphragm on one side of the cadaver. Save the side with the best dissection of arteries and nerves for review.
Retract the rectum, urinary bladder, prostate, and seminal vesicles medially.
Use blunt dissection to remove any remaining fat and connective tissue from the superior surface of the pelvic diaphragm.
To find the tendinous arch of the levator ani muscle (Figure 5.24A), palpate the medial surface of the ischial spine and then locate the obturator canal. The tendinous arch lies just inferior to a line connecting these two structures. Note that the tendinous arch is the superior edge of the pelvic diaphragm.
Identify the three muscles that form the levator ani muscle. The muscles are identified by their proximal attachments. Learn, but do not dissect, their distal attachments. Identify the following:

Puborectalis muscle – its proximal attachment is the body of the pubis. Its distal attachment is the puborectalis muscle of the opposite side (in a midline raphe). The puborectalis muscle forms the lateral boundary of the urogenital hiatus. The two puborectalis muscles form a “puborectal sling,” which causes the anorectal flexure at the ampulla of the rectum (Figure 5.21). During defecation, the puborectalis muscles relax, the anorectal flexure straightens, and the elimination of fecal matter is facilitated.
Pubococcygeus muscle – its proximal attachment is the body of the pubis. Its distal attachment is the coccyx and the anococcygeal raphe.
Iliococcygeus muscle – its proximal attachment is the tendinous arch. Its distal attachment is the coccyx and the anococcygeal raphe.

The levator ani muscle supports the pelvic viscera and resists increases in intra-abdominal pressure.
Identify the coccygeus muscle. The coccygeus muscle completes the pelvic diaphragm posteriorly. The proximal attachment of the coccygeus muscle is the ischial spine and its distal attachment
is the lateral border of the coccyx and the lowest part of the sacrum.
Place the fingers of one hand in the ischioanal fossa and the fingers of the other hand on the superior surface of the pelvic diaphragm. Palpate the thinness of the pelvic diaphragm.
Observe that the obturator internus muscle forms the lateral wall of the ischioanal fossa. The proximal attachment of the obturator internus muscle is the margin of the obturator foramen and inner surface of the obturator membrane. The distal attachment of the obturator internus muscle will be studied when the gluteal region is dissected. Superior to the tendinous arch of the levator ani muscle, the obturator internus muscle forms the lateral wall of the pelvic cavity. Inferior to the tendinous arch, the obturator internus muscle forms the lateral wall of the perineum.
Use your textbook to learn the general pattern of lymphatic drainage of the pelvis and the location of each of the following groups of lymph nodes:

Internal iliac nodes
External iliac nodes
Common iliac nodes
Sacral nodes
Lumbar nodes

Dissection Review

Use the dissected specimen to review the proximal attachment and action of each muscle of the pelvic diaphragm.
Review the relationship of the branches of the internal iliac artery to the pelvic diaphragm.
Review the relationship of the sacral plexus to the pelvic diaphragm.
Use an illustration to review the role played by the pelvic diaphragm in forming the boundary between the pelvic cavity and the perineum. Review the function of the pelvic diaphragm and perineal body in supporting the pelvic and abdominal viscera.
Use an illustration to review the lymphatic drainage from the pelvis and perineum. Realize that structures in the perineum (including the scrotum and the lower part of the anal canal) drain into superficial inguinal lymph nodes. The lymphatic drainage of the testis follows the testicular vessels to the lumbar chain of nodes, bypassing the perineal and pelvic drainage systems.
Review the formation of the thoracic duct to complete your understanding of the lymph drainage from this region.
Visit a dissection table with a female cadaver and perform a complete review of the dissected female pelvis.

RETURN TO TABLE OF CONTENTS

WEDNESDAY, JANUARY 27 – FEMALE PELVIC CAVITY AND PELVIC DIAPHRAGM

Female Pelvic Cavity

Dissection Overview

The female pelvic cavity contains the urinary bladder anteriorly, the female internal genitalia, and the rectum posteriorly (Figure 5.30). The term adnexa (L. adnexa, adjacent parts) refers to the ovaries, uterine tubes, and ligaments of the uterus. Removal of the uterus (hysterectomy), with or without the ovaries, is a common surgical procedure. If the uterus has been surgically removed from your cadaver, examine it in other cadavers.

The order of dissection will be as follows: The peritoneum will be studied in the female pelvic cavity. The pelvis will be sectioned in the midline and the cut surface of the sectioned pelvis will be studied. The uterus and vagina will be studied. The uterine tube will be traced from the uterus to the ovary. The ovary will be studied.

Dissection Instructions

Peritoneum

Using Figure 5.30 as a reference, examine the peritoneum in the female pelvis. Note that the peritoneum:

(1, 2) Passes from the anterior abdominal wall superior to the pubis
(3) Covers the superior surface of the urinary bladder
(4) Passes from the superior surface of the urinary bladder to the uterus where it forms the vesicouterine pouch
(5) Covers the fundus and body of the uterus and contacts the wall of the posterior part of the vaginal fornix
(6) Forms the rectouterine pouch between the uterus and the rectum
(7) Covers the anterior surface and sides of the rectum
(8) Forms the sigmoid mesocolon beginning at the level of the third sacral vertebra

Laterally, a paravesical fossa is apparent on each side of the urinary bladder. Further posteriorly, a pararectal fossa is apparent on each side of the rectum.
Identify the broad ligament of the uterus. The broad ligament of the uterus is formed by two layers of peritoneum that extend from the lateral side of the uterus to the lateral pelvic wall. The uterine tube is contained within the superior margin of the broad ligament. The broad ligament has three parts (Figure 5.31):

Mesosalpinx (Gr. salpinx, tube) – supports the uterine tube
Mesovarium – attaches the ovary to the posterior aspect of the broad ligament
Mesometrium – the part of the broad ligament that is below the attachment of the mesovarium

The tissue enclosed between the two layers of the broad ligament is called parametrium (Gr. para, beside; metra, womb, uterus).
Identify the round ligament of the uterus, which is visible through the anterior layer of the broad ligament (Figure 5.31). Observe that the round ligament of the uterus passes over the pelvic brim and exits the abdominal cavity by passing through the deep inguinal ring, lateral to the inferior epigastric vessels. The round ligament of the uterus passes through the inguinal canal and ends in the labium majus.
Identify the ovarian ligament, which is a fibrous cord within the broad ligament that connects the ovary to the uterus.
Identify the suspensory ligament of the ovary, which is a peritoneal fold that covers the ovarian vessels. The suspensory ligament of the ovary extends into the greater pelvis from the superior aspect of the ovary.

IN THE CLINIC: Pelvic Peritoneum

As the urinary bladder fills, the peritoneal reflection from the anterior abdominal wall to the bladder is elevated above the level of the pubis. A filled urinary bladder can be approached with a needle superior to the pubis without entering the peritoneal cavity.

Section of the Pelvis

Begin this dissection with a new scalpel blade.
Use your hand to position the uterus in the midline. Use a scalpel to divide the uterus in its median plane. Extend the cut through the cervix and into the fornix of the vagina.
Beginning posterior to the pubic symphysis, make a midline cut through the superior surface of the urinary bladder. Open the bladder and sponge the interior, if necessary.
Identify the internal urethral orifice and insert a probe. Using the probe as a guide, cut through the inferior part of the bladder, dividing the urethra.
Extend the midline cut in the posterior direction. Cut through the anterior and posterior walls of the rectum and the distal part of sigmoid colon. Sponge them clean.
In the perineum, insert the tip of a probe into the external urethral orifice. Use the probe as a guide to make a midline cut through the clitoris, dividing it into right and left sides. Extend this cut posteriorly, dividing the urethra and vagina into right and left sides.
In the midline, cut through the perineal membrane, perineal body, and anal canal. Extend the cut to the tip of the coccyx.
Use a saw to make two cuts in the midline:

Pubic symphysis – cut through the pubic symphysis from anterior to posterior.
Sacrum – turn the cadaver to the prone position. Cut through the sacrum from posterior to anterior. Do not allow the saw to pass between the soft tissue structures that were cut with the scalpel. Spread the opening and extend the midline cut as far superiorly as the body of the third lumbar vertebra.

Return the cadaver to the supine position. Cut the right renal arteries and veins (do not cut the ureter) and place the right kidney in the pelvic cavity to protect the ureter from the subsequent transverse cut. Repeat for the left kidney.
To mobilize the lower limbs, use a scalpel to make a transverse cut through the soft tissues at vertebral level L3/L4
In the transverse plane, use the saw to cut horizontally through the intervertebral disc between L3 and L4. Now, the lower limbs can be removed.
Clean the rectum and anal canal.

Female Internal Genitalia

Study the cut surface of the sectioned specimen. Use an illustration to guide you.
Trace the sectioned urethra anteroinferiorly from the urinary bladder to the external urethral orifice. Attempt to identify the external urethral sphincter muscle that surrounds the urethra. The external urethral sphincter muscle may be difficult to see.
In the sectioned specimen, observe the vagina. Identify the vaginal fornix. The vaginal fornix has four parts: anterior, lateral (2), and posterior (Figure 5.32). Observe that the anterior vaginal wall is shorter than the posterior vaginal wall.

Observe that the posterior wall of the vagina (near the posterior part of the vaginal fornix) is in contact with the peritoneum that lines the rectouterine pouch.
Study the uterus (Figure 5.32). Observe that the uterus is tilted approximately 90° anterior to the axis of the vagina (anteverted). The position of the uterus changes as the bladder fills, and during pregnancy.
Identify the following features of the uterus (Figure 5.32A):

Fundus – the rounded part of the body that lies superior to the attachments of the uterine tubes
Body – the part of the uterus between the fundus and the cervix. The vesical surface of the body of the uterus faces the vesicouterine pouch and the intestinal surface faces the rectouterine pouch. Note that the broad ligament is attached to the lateral surface of the body of the uterus.
Isthmus – the narrowed portion of the body that is superior to the cervix.
Cervix – the thick-walled portion of the uterus that protrudes into the vaginal canal.

Identify the uterine cavity. In a coronal section, it is triangular (Figure 5.32A). In a sagittal section, it is a slit (Figure 5.32B).
Note that the uterine mucosa is called endometrium. The thick muscular wall of the uterus is called myometrium. The peritoneal covering on the surface of the uterus is called perimetrium (Gr. pari, around). The tissues within the broad ligament are called parametrium (Gr. para, beyond).
Identify the uterine tube (Figure 5.32A). Use your fingers to follow the uterine tube as it passes laterally within the mesosalpinx. Observe:

Isthmus – the narrow, medial one-third of the uterine tube
Ampulla – the widest and longest part of the uterine tube
Infundibulum – the funnel-like end of the uterine tube
Fimbriae – multiple processes that surround the distal margin of the infundibulum

Observe the ovary. The ovary is ovoid, with a tubal (distal) extremity and a uterine (proximal) extremity. The ovarian vessels enter the tubal extremity of the ovary, and the ligament of the ovary is attached to the uterine extremity.
The ovary sits in the ovarian fossa. The ovarian fossa is a shallow depression in the lateral pelvic wall bounded by the ureter, external iliac vein, and uterine tube.
Review the abdominal origin and course of the ovarian vessels. Note that they pass through the suspensory ligament of the ovary.
The endopelvic fascia (extraperitoneal fascia) contains condensations of connective tissue that passively support the uterus. Study an illustration and note the following:

Uterosacral (sacrogenital) ligament – extends from the cervix to the sacrum. The uterosacral ligament underlies the uterosacral fold.
Transverse cervical ligament (cardinal ligament) – extends from the cervix to the lateral wall of the pelvis.
Pubocervical (pubovesical) ligament – extends from the pubis to the cervix.

Dissection Review

Review the position of the female pelvic viscera within the lesser pelvis. Visit a dissection table with a male cadaver and observe the position of the male pelvic viscera.
Review the peritoneum in the female pelvic cavity. Visit a dissection table with a male cadaver and compare differences in the female and male peritoneum (Figs. 5.17 and 5.30).
Trace the round ligament of the uterus from the superficial inguinal ring to the uterus.
Visit a table with a male cadaver and trace the ductus deferens from the epididymis to the ejaculatory duct, noting its relationships to vessels, nerves, the ureter, and the seminal vesicle.
Compare the pelvic course of the ductus deferens with the pelvic course of the round ligament of the uterus.
Review the parts of the broad ligament and review the function of the endopelvic fascia in passive support of the uterus.

Urinary Bladder, Rectum, and Anal Canal

Dissection Overview

The urinary bladder is a reservoir for urine. When empty, it is located within the pelvic cavity. When filled, it extends into the abdominal cavity. The urinary bladder is a retroperitoneal organ that is surrounded by endopelvic fascia. Between the pubic symphysis and the urinary bladder there is a potential space called the retropubic space (prevesical space) (Figure 5.30). The retropubic space is filled with fat and loose connective tissue that accommodates the expansion of the urinary bladder. The pubovesical ligament is a condensation of fascia that ties the neck of the urinary bladder to the pubis across the retropubic space. The pubovesical ligament defines the inferior limit of the retropubic space (Figure 5.30). The lower one-third of the rectum is surrounded by endopelvic fascia. The middle and upper thirds of the rectum are partially covered by peritoneum (Figure 5.30).

Dissection Instructions

Urinary Bladder

Identify the parts of the urinary bladder (Figure 5.33):

Apex – the pointed part directed toward the anterior abdominal wall. The apex of the urinary bladder can be identified by the attachment of the urachus.

Body – between the apex and fundus.
Fundus – the inferior part of the posterior wall, also called the base of the bladder. In the female the fundus is related to the vagina and cervix.
Neck – where the urethra exits the urinary bladder. In the neck of the urinary bladder, the wall thickens to form the internal urethral sphincter, which is an involuntary muscle.

Identify the four surfaces of the urinary bladder (Figure 5.33):

Superior – covered by peritoneum
Posterior – covered by peritoneum on its superior part and by the endopelvic fascia on its inferior part
Inferolateral (2) – covered by endopelvic fascia

Examine the wall of the urinary bladder and note its thickness. The wall of the urinary bladder consists of bundles of smooth muscle called the detrusor muscle (L. detrudere, to thrust out).
Identify the trigone on the inner surface of the fundus (Figure 5.34). The angles of the trigone are the internal urethral orifice and the two orifices of the ureters. The internal urethral orifice is located at the most inferior point in the urinary bladder.
Observe that the mucous membrane over the trigone is smooth. The mucous membrane lining the other parts of the urinary bladder lies in folds when the bladder is empty but will accommodate expansion.
Insert the tip of a probe into the orifice of the ureter and observe that the ureter passes through the wall of the urinary bladder in an oblique direction. When the urinary bladder is full (distended), the pressure of the accumulated urine flattens the part of the ureter that is within the wall of the bladder and prevents reflux of urine into the ureter.

Find the ureter where it crosses the external iliac artery or the bifurcation of the common iliac artery. Use a probe to follow the ureter to the fundus of the urinary bladder. Observe that the ureter crosses inferior to the uterine artery and superior to the vaginal artery.

IN THE CLINIC: Kidney Stones

Rectum and Anal Canal

1. Recall that the rectum begins at the level of the third sacral vertebra. Observe the sectioned pelvis and note that the rectum follows the curvature of the sacrum.

2. Identify the ampulla of the rectum (Figure 5.35). At the ampulla, the rectum bends approximately 80° posteriorly (anorectal flexure) and is continuous with the anal canal.

4. Observe that the anal canal is only 2.5 to 3.5 cm in length. The anal canal passes out of the pelvic cavity and enters the anal triangle of the perineum.

5. Examine the inner surface of the anal canal (Figure 5.35). Note that the mucosal features of the anal canal may be difficult to identify in older individuals, but attempt to identify the following:

Anal columns – 5 to 10 longitudinal ridges of mucosa in the proximal part of the anal canal. The anal columns contain branches of the superior rectal artery and vein.
Anal valves – semilunar folds of mucosa that unite the distal ends of the anal columns. External to each anal valve is a small pocket called an anal sinus.
Pectinate line – the irregular line formed by all of the anal valves.

6. The anal sphincter muscles surround the anal canal. Identify the external anal sphincter muscle and the internal anal sphincter muscle in the sectioned specimen (Figure 5.35). The longitudinal muscle of the anal canal separates the two sphincter muscles. If you have difficulty identifying them, use a new scalpel blade to cut another section through the wall of the anal canal to improve the clarity of the dissection.

IN THE CLINIC; Hemorrhoids

Dissection Review

Use the dissected specimen to review the features of the urinary bladder, rectum, and anal canal.
Review the relationships of the uterus, vagina, and ureters to the rectum and fundus of the urinary bladder.
Visit a dissection table with a male cadaver and review the relationships of the seminal vesicles, ampulla of the ductus deferens, and ureters to the rectum and fundus of the urinary bladder.
Review the kidney, the abdominal course of the ureter, the pelvic course of the ureter, and the function of the urinary bladder as a storage organ.
Review the female urethra. Visit a table with a male cadaver and review the parts of the male urethra.
Review all parts of the large intestine and recall its function in absorption of water and in compaction and elimination of fecal material.
Recall that the external anal sphincter muscle is composed of skeletal muscle and is under voluntary control, whereas the internal anal sphincter muscle is composed of smooth muscle and is involuntary.

Internal Iliac Artery and Sacral Plexus

Dissection Overview

Anterior to the sacroiliac articulation, the common iliac artery divides to form the external and internal iliac arteries (Figure 5.36). The external iliac artery distributes to the lower limb and the internal iliac artery distributes to the pelvis. The internal iliac artery has the most variable branching pattern of any artery, and it is worth noting at the outset of this dissection that you must use the distribution of the branches to identify them, not their pattern of branching.

The order of dissection will be as follows: The branches of the anterior division of the internal iliac artery will be identified. The branches of the posterior division of the internal iliac artery will be identified. The nerves of the sacral plexus will be dissected. Finally, the pelvic portion of the sympathetic trunk will be dissected.

Dissection Instructions

Blood Vessels

The internal iliac vein is typically plexiform. To clear the dissection field, remove all tributaries to the internal iliac vein.
Identify the common iliac artery and follow it distally until it bifurcates.
Identify the internal iliac artery. Use blunt dissection to follow the internal iliac artery into the pelvis.
Identify the branches of the anterior division of the internal iliac artery (Figure 5.36):

Umbilical artery – in the medial umbilical fold, find the medial umbilical ligament (the obliterated portion of the umbilical artry) and use blunt dissection to trace it posteriorly to the umbilical artery. Note that several superior vesical arteries arise from the inferior surface of the umbilical artery and descend to the superolateral aspect of the urinary bladder.
Obturator artery – passes through the obturator canal. Find the obturator artery where it enters the obturator canal in the lateral wall of the pelvis, and follow the artery posteriorly to its origin. In about 20% of cases, an aberrant obturator artery (a branch of the external iliac artery) crosses the pelvic brim and is at risk of injury during surgical repair of a femoral hernia.
Uterine artery – courses along the inferior attachment of the broad ligament. Use blunt dissection to trace it to the lateral aspect of the uterus and note that it passes superior to the ureter. The uterine artery divides into a large superior branch to the body and fundus of the uterus and a smaller branch to the cervix and vagina. Observe the close relationship of the lateral part of the vaginal fornix to the uterine artery. In a living person, the pulsations of the uterine artery may be felt through the lateral part of the vaginal fornix.
Vaginal artery – passes across the floor of the pelvis, inferior to the ureter. The vaginal artery supplies the vagina and the urinary bladder. Note that the ureter passes between the vaginal artery and the uterine artery.
Middle rectal artery – courses medially toward the rectum. To confirm the identity of the middle rectal artery, follow it to the rectum.
Internal pudendal artery – exits the pelvic cavity by passing through the greater sciatic foramen inferior to the piriformis muscle. The internal pudendal artery often arises from a common trunk with the inferior gluteal artery.
Inferior gluteal artery – usually passes out of the pelvic cavity between ventral rami S2 and S3. The inferior gluteal artery exits the pelvis by passing through the greater sciatic foramen inferior to the piriformis muscle. The inferior gluteal artery may share a common trunk with the internal pudendal artery, or less commonly, with the superior gluteal artery.

Identify the branches of the posterior division of the internal iliac artery (Figure 5.36):

Iliolumbar artery – passes posteriorly, then ascends between the lumbosacral trunk and the obturator nerve. It may arise from a common trunk with the lateral sacral artery.
Lateral sacral artery – gives rise to a superior branch and an inferior branch. Observe the inferior branch that passes anterior to the sacral ventral rami.
Superior gluteal artery – usually exits the pelvic cavity by passing between the lumbosacral trunk and the ventral ramus of spinal nerve S1.

Use an illustration to study the vesical venous plexus, uterine venous plexus, vaginal venous plexus, and rectal venous plexus. All of these plexuses drain into the internal iliac vein.

IN THE CLINIC: Uterine Artery

The close proximity of the ureter and the uterine artery near the lateral fornix of the vagina is of clinical importance. During hysterectomy, the uterine artery is tied off and cut. The ureter may be unintentionally clamped, tied off, and cut where it crosses the uterine artery. This would have serious consequences for the corresponding kidney. To recall this relationship, use the mnemonic device “water under the bridge.” The “water” is urine; the “bridge” is the uterine artery.

Nerves

The somatic plexuses of the pelvic cavity are the sacral plexus and coccygeal plexus. These plexuses are located between the pelvic viscera and the lateral pelvic wall, within the endopelvic fascia. These somatic nerve plexuses are formed by contributions from ventral rami of spinal nerves L4 to S4. The primary visceral nerve plexus of the pelvic cavity is the inferior hypogastric plexus. It is formed by contributions from the hypogastric nerves, sympathetic trunks, and pelvic splanchnic nerves.

Use your fingers to dissect the rectum from the anterior surface of the sacrum and coccyx.
Retract the rectum medially and identify the sacral plexus of nerves. The sacral plexus is closely related to the anterior surface of the piriformis muscle. Verify the following (Figure 5.37):

The lumbosacral trunk (ventral rami of L4 and L5) joins the sacral plexus.
The ventral rami of S2 and S3 emerge between the proximal attachments of the piriformis muscle.
The sciatic nerve is formed by the ventral rami of spinal nerves L4 through S3. The sciatic nerve exits the pelvis by passing through the greater sciatic foramen, usually inferior to the piriformis muscle.
The superior gluteal artery usually passes between the lumbosacral trunk and the ventral ramus of spinal nerve S1, and exits the pelvis by passing superior to the piriformis muscle.
The inferior gluteal artery usually passes between the ventral rami of spinal nerves S2 and S3. The inferior gluteal artery exits the pelvis by passing inferior to the piriformis muscle.
The pudendal nerve receives a contribution from the ventral rami of spinal nerves S2, S3, and S4. The pudendal nerve exits the pelvis by passing inferior to the piriformis muscle.

Identify the pelvic splanchnic nerves (nervi erigentes). Pelvic splanchnic nerves are branches of the ventral rami of spinal nerves S2 through S4 (Figure 5.37). Pelvic splanchnic nerves carry preganglionic parasympathetic axons for the innervation of pelvic organs and the distal gastrointestinal tract (from the left colic flexure through the anal canal).
The sacral portion of the sympathetic trunk is located on the anterior surface of the sacrum, medial to the ventral sacral foramina. Identify the following:

Sympathetic trunk – continues from the abdominal region into the pelvis. The sympathetic trunks of the two sides join in the midline near the level of the coccyx to form the ganglion impar.
Gray rami communicantes – connect the sympathetic ganglia to the sacral ventral rami. Each gray ramus communicans carries postganglionic sympathetic fibers to a ventral ramus for distribution to the lower extremity and the perineum.
Sacral splanchnic nerves – arise from two or three of the sacral sympathetic ganglia and pass directly to the inferior hypogastric plexus. Sacral splanchnic nerves carry sympathetic fibers that distribute to the pelvic viscera.

IN THE CLINIC: Pelvic Nerve Plexuses

The pelvic splanchnic nerves (parasympathetic outflow of S2, S3, and S4) are closely related to the lateral aspects of the rectum. The inferior hypogastric plexus is located in the connective tissue lateral to the uterus. These autonomic nerve plexuses can be injured during surgery, causing loss of bladder control.

Dissection Review

Review the abdominal aorta and its terminal branches.
Use the dissected specimen to review the branches of the internal iliac artery. Review the region supplied by each branch.
Review the relationship of the uterine and vaginal arteries to the ureter.
Review the formation of the sacral plexus and the branches that were dissected in the pelvis.
Use the dissected specimen and an illustration to review the course of the pudendal nerve from the pelvic cavity to the urogenital triangle.

Pelvic Diaphragm

Dissection Overview

The pelvic diaphragm is the muscular floor of the pelvic cavity. The pelvic diaphragm is formed by the levator ani muscle and coccygeus muscle plus the fasciae covering their superior and inferior surfaces (Figure 5.38A,B). The pelvic diaphragm extends from the pubic symphysis to the coccyx. Laterally, the pelvic diaphragm is attached to the fascia covering the obturator internus muscle. The urethra and vagina and the anal canal pass through midline openings in the pelvic diaphragm called the urogenital hiatus and anal hiatus, respectively.

Dissection Instructions

Perform the dissection of the pelvic diaphragm on one side of the cadaver. Save the side with the best dissection of arteries and nerves for review.
Retract the urinary bladder, uterus, and rectum toward the midline.
Use blunt dissection to remove any remaining fat and connective tissue from the superior surface of the pelvic diaphragm.
To find the tendinous arch of the levator ani muscle (Figure 5.38A), palpate the medial surface of the ischial spine and then locate the obturator canal. The tendinous arch lies just inferior to a line connecting these two structures. Note that the tendinous arch is the superior edge of the pelvic diaphragm.
Identify the three muscles that form the levator ani muscle. The muscles are identified by their proximal attachments. Learn, but do not dissect, their distal attachments. Identify the following:

Puborectalis muscle – its proximal attachment is the body of the pubis. Its distal attachment is the puborectalis muscle of the opposite side (in a midline raphe). The puborectalis muscle forms the lateral boundary of the urogenital hiatus. The two puborectalis muscles form a “puborectal sling,” which causes the anorectal flexure at the ampulla of the rectum (Figure 5.35). During defecation, the puborectalis muscles relax, the anorectal flexure straightens, and the elimination of fecal matter is facilitated.
Pubococcygeus muscle – its proximal attachment is the body of the pubis. Its distal attachment is the coccyx and the anococcygeal raphe.
Iliococcygeus muscle – its proximal attachment is the tendinous arch. Its distal attachment is the coccyx and the anococcygeal raphe.

The levator ani muscle supports the pelvic viscera and resists increases in intra-abdominal pressure.
Identify the coccygeus muscle. The coccygeus muscle completes the pelvic diaphragm posteriorly. The proximal attachment of the coccygeus muscle is the ischial spine and its distal attachment is the lateral border of the coccyx and the lowest part of the sacrum.
Place the fingers of one hand in the ischioanal fossa and the fingers of the other hand on the superior surface of the pelvic diaphragm. Palpate the thinness of the pelvic diaphragm.
Observe that the obturator internus muscle forms the lateral wall of the ischioanal fossa. The proximal attachment of the obturator internus muscle is the margin of the obturator foramen and inner surface of the obturator membrane. The distal attachment of the obturator internus muscle will be studied when the gluteal region is dissected. Superior to the tendinous arch of the levator ani muscle, the obturator internus muscle forms the lateral wall of the pelvic cavity. Inferior to the tendinous arch, the obturator internus muscle forms the lateral wall of the perineum.
Use your textbook to learn the general pattern of lymphatic drainage of the pelvis and the location of each of the following groups of lymph nodes:

Internal iliac nodes
External iliac nodes
Common iliac nodes
Sacral nodes
Lumbar nodes

Dissection Review

Use the dissected specimen to review the proximal attachment and action of each muscle of the pelvic diaphragm.
Review the relationship of the branches of the internal iliac artery to the pelvic diaphragm.
Review the relationship of the sacral plexus to the pelvic diaphragm.
Use an illustration to review the role played by the pelvic diaphragm in forming the boundary between the pelvic cavity and the perineum. Review the function of the pelvic diaphragm and perineal body in supporting the pelvic and abdominal viscera.
Use an illustration to review the lymphatic drainage from the pelvis and perineum. Realize that structures in the perineum (including the labia majora and the lower part of the anal canal) drain into superficial inguinal lymph nodes. The lymphatic drainage of the ovary follows the ovarian vessels to the lumbar chain of nodes, bypassing the pelvic drainage systems.
Review the formation of the thoracic duct to complete your understanding of the lymph drainage from this region.
Visit a dissection table with a male cadaver and perform a complete review of the dissected male pelvis.

RETURN TO TABLE OF CONTENTS

FOCUS QUESTIONS and ANSWERS

1. Note the difference between male and female in the subpubic angle, the angle formed by the subpubic arch. What are other sex differences in the pelvic skeleton?

2. Define the rectum.

3. Define and note the flexure between rectum and anal canal. What muscle assists in maintaining this flexure?

4. On the sagittally-sectioned female specimen, trace the peritoneum from the ventral abdominal wall; examining the vesicouterine pouch and its manner of reflection from the bladder to the uterus. Onto what part of uterus does it reflect?

5. Trace the peritoneum across the uterus and define the rectouterine pouch. Note peritoneum on the posterior wall of the vagina. From what point does the peritoneum reflect to the rectum? What is the significance of this?

6. Within the broad ligament, locate the ovarian ligament and the round ligament of the uterus. Consider development and continuities of these structures.

7. Locate and define the peritoneal fold called the suspensory ligament of the ovary. What does it contain?

8. Strip the peritoneum from the suspensory ligament of the ovary on one side and trace the ovarian artery and vein. What are their sources?

9. What is the complete area of distribution of the ovarian artery?

10. Locate a ureter. Note its relation to uterine artery. Trace it to the bladder and posteriorly to the brim of the pelvis, noting course, relation to peritoneum, and blood supply.

11. Trace the round ligament from the uterus to the deep inguinal ring. Where does it attach?

12. What structures support the uterus?

13. Explore the female urethra, noting length, sphincter muscle, and relation to vagina. Note specifically the relation of the orifice to the anterior vaginal wall. What is the significance ?

14. Define the ampulla of the ductus deferens. Is it covered by peritoneum?

15. What is the rectovesical pouch?

16. Where does the transition of the epididymis to the ductus deferens occur?

17. Locate the anterior division of the internal iliac artery and note how it terminates by dividing into the inferior gluteal and the internal pudendal arteries. These exit the pelvis below the lower border of the piriformis muscle. What are other relations?

18. Do you have an "aberrant obturator artery", which arises from the inferior epigastric artery and accompanies the obturator nerve?

19. Locate the sympathetic trunk entering the pelvis along the medial border of the pelvic sacral foramina. Note number of ganglia, gray rami communcantes, and sacral splanchnic nerves.

20. How many pelvic splanchnic nerves are there?

21. What is the puborectalis muscle? What is its significance?

22. Define the urogenital hiatus. What does it transmit?

23. Do you find muscular (deep) branches of the perineal nerves?

24. What is the source and drainage of the deep dorsal vein of the clitoris/penis and the dorsal veins and arteries of the clitoris/penis?

25. What is the function of the perineal membrane?

26. What is the source of the deep (central) artery of the clitoris/penis?

27. What gland is embedded in the sphincter urethrae muscle in males?

RETURN TO TABLE OF CONTENTS