Lab Manual - Perineum & External Genitalia

Learning Objectives:

Upon completion of this session, the student will be able to:

  1. Trace the skeletal and ligamentous boundaries of the perineum, and define the anal and urogenital triangles. (explanation)
  2. Describe the position and boundaries of the ischioanal fossa. (explanation)
  3. Describe the structure, contents, and course of the pudendal canal. (explanation)
  4. Trace the branching pattern of the internal pudendal vessels and the pudendal nerve. (explanation)
  5. Differentiate between the internal and external anal sphincters in structure and function. (explanation)
  6. Differentiate between male and female urethrae. (explanation)
  7. Identify the components of the external genital organs and give the homologues in each of both sexes. (explanation)
  8. Describe structure and function of the erectile bodies. (explanation)
  9. Trace the nerve and blood supply to the external genital organs. (explanation)
  10. Trace the lymphatic drainage of the perineum. (explanation)

Readings and Modules:

Procedure:

Dissection is optional.

You are responsible for the information in this session and should be able to identify all structures on the list of review items. You may choose to do the dissection on your cadaver and/or you may utilize prossected specimens, plastinated specimens, and models to facilitate your understanding of this region.

1. Skin the ischioanal fossa and remove the fat. Identify the sacrotuberal and sacrospinal ligaments and the inferior rectal nerves and vessels. (Play movie; View images: N 353, 357, 358, 359, 377, 379, 380, 381, 395, 402 403, 404, 405, 411, 413, 502, 503, TG 3-07, 3-26, 6-06, 6-15A, 6-15B, 6-15C, 6-23A, 6-23B, 6-24A, 6-24B, 6-26A, 6-26B, 6-28, 6-29A, 6-29B, 6-30A, 6-30B)

Remove the skin from the anal triangle. Care should be taken when skinning around the anus because the external anal sphincter muscle is in contact with the skin. Clean and identify the external anal sphincter.

Using blunt dissection through the fat of the ischioanal (ischiorectal) fossa, locate the inferior rectal vessels and nerves, supplying the external anal sphincter. On the lateral side, follow the walls of the ischioanal fossa and remove all of the fat within the fossa. To do this, identify the inferior border of the gluteus maximus muscle and the ischial tuberosity and follow these surfaces deeply within the ischioanal fossa until the fat wedge is free. Note how gluteus maximus overhangs the ischioanal fossa. Reflect the fibers of gluteus maximus that originate from the sacrotuberal ligament. Define all boundaries of the ischioanal fossa. Note that the lateral wall is the fascia of the obturator internus muscle, and cut the sacrotuberal ligament from its attachment on the ischial tuberosity. Beneath the sacrotuberal ligament, identify the sacrospinal ligament and the greater and lesser sciatic foramina.

2. Identify the pudendal canal and pudendal neurovascular bundle. (Play movie; View images: N 402, 403, 404, 405, 410, 411, 413, 497, 499, 503, TG 3-25A, 3-25B, 3-26, 6-17A, 6-17B, 6-19, 6-29A, 6-29B, 6-30)

Identify the pudendal neurovascular bundle passing around the sacrospinal ligament. Pick up the inferior rectal vessels and nerves, and gently pull toward the midline. This tension will elevate the wall of the pudendal canal so that it may be visualized. Open the canal and identify the pudendal nerve, the internal pudendal artery and veins. Note how far (deep) this canal is from the tip of the ischial tuberosity.

3. FEMALE: Skin the urogenital triangle. Identify the pudendal neurovascular branches. Clean the erectile bodies and reflect them from their attachments on one side. Identify the perineal membrane and sphincter urethrae m. (Play movie; View images: N 265, 344, 357, 377, 379A, 379B, 381, 395, 404, 413, TG 6-08, 6-24, 6-25, 6-29, 6-27, 6-28, 6-29, 6-30, 6-32)

Remove the skin of the perineum from a longitudinal incision along the medial border of the labia majora laterally to the ischiopubic ramus.

The subcutaneous tissue of the perineum consists of a superficial fatty and a deeper membranous layer. Dissect through the fat of the labia majora and locate the posterior labial nerve, arteries and veins (branches of the perineal nerve from pudendal nerve and internal pudendal artery and vein, respectively). Remove the excess fat and reflect the membranous plane laterally to the ischiopubic ramus.

Remove the muscular fascia; dissect and identify the ischiocavernosus and bulbospongiosus muscles. Great care must be taken because the muscles are very thin and delicate. Note specifically the relations of these muscles to the cavernous bodies. Clear the perineal body. Reflect the bulbospongiosus muscle from the perineal body on one side, carefully lifting it from the surface of the vestibular bulb, and noting the manner in which the muscle ends at the base of the shaft of the clitoris. Do you find muscular branches (deep) of the perineal nerves? Look for the greater vestibular glands at the posterior margin of the vestibular bulbs, deep to the bulbospongiosus muscles. Reflect the ischiocavernosus muscle on the same side and expose the crus of the clitoris. Examine the crus and trace the corpus cavernosum clitoridis forward until it unites with the corpus cavernosum of the opposite side to form the shaft of the clitoris. On the dorsum of the shaft of the clitoris, locate the deep dorsal vein, and the dorsal nerves and dorsal arteries of the clitoris. Examine the glans clitoridis.

Cut the crus of the clitoris from the ischiopubic ramus on one side, and free the vestibular bulb on that side from its attachment to the perineal membrane. As you do this, try to identify the deep artery of the clitoris and the artery to the bulb. Crossing between the arcuate pubic ligament and the perineal membrane is the deep dorsal vein of the clitoris, while the dorsal arteries and nerves of the clitoris pass through the anterosuperior portion of the perineal membrane. Source or drainage of each? Section the corpus cavernosum clitoridis and the vestibular bulb, examining the erectile tissue and tunica albuginea.

Now examine the perineal membrane, its extent and attachments. Consider its function. Examine the vagina passing through the membrane, noting its relationship to the membranous urethra and the sphincter urethrae muscle.

4. MALE: Skin the urogenital triangle. Identify the pudendal neurovascular branches. Clean the erectile bodies and reflect them from their attachments on one side. Identify the perineal membrane and sphincter urethrae m. (Play movie; View images: N 265, 266, 359, 362, 364, 365, 379A, 379B, 380, 381A, 381B, 382A, 382B, 383, 385A, 385B, 387, 404, 405A, 405B, 407, 411, TG 5-02, 5-37, 6-09A, 6-09B, 6-10, 6-26, 6-27, 6-28, 6-29, 6-30, 6-31A, 6-31B, 6-32, 6-33, 6-34)

Remove the skin from the penis, scrotum and perineum laterally to the ischiopubic ramus. Note that the subcutaneous tissue of the penis and scrotum contains no fat. In the scrotum this layer, the tunica dartos scroti, contains smooth muscle, often giving it a pinkish color. Pull the half scrotum, with its contained testis, toward the ventral abdominal wall, revealing the complete perineum and the ventral surface of the penis.

The subcutaneous tissue of the perineum consists of a fatty and a membranous layer. Carefully reflect both to one side, and continue reflecting from the shaft of the penis. Within the subcutaneous tissue locate posterior scrotal nerves, arteries and veins (branches of the perineal nerve from pudendal nerve and internal pudendal artery and vein, respectively).

Dissect the ischiocavernosus and bulbospongiosus muscles and note how the deep fascia of these muscles completely invests the shaft of the penis (deep penile fascia). Remove this muscular fascia to reveal the ischiocavernosus and bulbospongiosus muscles covering the crura and bulb of the penis. Reflect one ischiocavernosus muscle and expose the crus of the corpus cavernosum penis. Reflect the bulbospongiosus muscle from the midline, noting the manner in which the muscle covers the bulb of the corpus spongiosum and encircles the root of the penis. Do you find muscular branches (deep) of the perineal nerves? Identify and trace the corpus spongiosum, its bulb, and at the tip of the penis, the glans. Trace the corpora cavernosa penis, noting how the right and left unite to form the shaft of the penis. On the dorsum of the penis locate and identify the deep dorsal vein, and the dorsal arteries and nerves. On one side, cut the penis transversely through the shaft and identify the structure and relationship of the erectile bodies and the tunica albuginea (note differences between corpus spongiosum and cavernosum). Note central or deep artery of penis. Source?

Cut the crus of the penis from the ischiopubic ramus on one side, and free the bulb on this side from its attachment to the perineal membrane. As you do this, try to identify the deep artery of the penis and the artery to the bulb. In midsagittal section, examine the penile (spongy) urethra, its bulb and navicular fossa. Crossing between the arcuate pubic ligament and the anterior border of the perineal membrane is the deep dorsal vein of the penis, while the dorsal arteries and veins of the penis pass through the anterosuperior portion of the perineal membrane. Source or drainage of each?

Now examine the perineal membrane, its extent and attachments. Consider its function. Examine the sphincter urethrae muscle. What gland is embedded in this muscle (in the male)? What are the bulbourethral glands? Review the parts of the male urethra (prostatic, membranous, and spongy or penile).

Review the lymphatics of the pelvis and perineum.