Prelab Images - Perineum & External Genitalia

Prelab should consist of reading the lab manual and dissector answers and viewing the dissection video. To begin your study, you may find it useful to look over the Netter's or LWW Atlas images listed below.

Step 1. Skin the ischioanal fossa and remove the fat. Identify the sacrotuberal and sacrospinal ligaments and the inferior rectal nerves and vessels. (Play movie)

Remove the skin from the anal triangle (boundaries of this triangle are reviewed in plate N380 or TG6-24A and TG6-24B). Be careful when skinning around the external anal sphincter muscle because it is very superficial (N379, N381 or TG6-15A, and N395 or TG6-15B and TG6-15C).

Next, use blunt dissection in the ischioanal fossa (identified in plate N377 or TG6-28). Look for the inferior rectal arteries and nerves while blunt dissecting. Plate N414 or TG6-28 shows the inferior rectal nerves branching off the pudendal nerve and plates N411 or TG6-30A and N413 or TG6-30B show the inferior rectal nerves innervating the external anal sphincter. Plates N402 and N403 or TG6-28 show the inferior rectal arteries branching off of the internal pudendal artery and plates N404 or TG6-29A and TG6-29B and N405 show the inferior rectal arteries coursing towards the external anal sphincter muscle. Plates N377 or TG6-26A and N380 or TG6-26B identify the inferior fibers of gluteus maximus, the ischial tuberosity, and the sacrotuberous ligament. You will need to peel gluteus maximus off of the sacrotuberous ligament and reflect it posteriorly to open up the area of dissection (in order to trace the pudendal vessels). Plate N377 or TG6-28 labels the obturator internus fascia at the lateral border of the ischioanal fossa (also see plates N357 or TG6-23A and N359 or TG6-23B for this muscle). Cut the sacrotuberal ligament from its attachment to the ischial tuberosity (N344 or TG6-23A, N358 or TG6-23B, N377 or TG6-28). Beneath the sacrotuberal ligament identify the sacrospinous ligament (N344 or TG6-23A, N359 or TG6-23B, N357 or TG6-06, N503 or TG3-07) and the greater and lesser sciatic foramina (N353 or TG6-06 and N503 or TG3-07). Plates N502 or TG3-26 and N503 review the structures passing through the greater and lesser sciatic foramina.

Step 2. Identify the pudendal canal and pudendal neurovascular bundle. (Play movie)

Plate N503 or TG3-26 shows the pudendal nerve near the sacrospinal ligament (you may have found it here earlier during the gluteal region lab, and it may help to trace the nerve from this location). Plates N402 or TG6-17A and N403 or TG6-17B show the origin of the internal pudendal artery and plates N404 or TG6-29A and N405 or TG6-29B show the internal pudendal artery traveling through the pudendal canal and distributing through the perineum. The internal pudendal arteries are accompanied by the internal pudendal veins. Plates N497 or TG3-25A, N499 or TG3-25B and N410 or TG6-19 show the origin of the pudendal nerve from the sacral plexus. Plates N411 and N413 or TG6-30 show the pudendal nerve traveling through the pudendal canal and distributing throughout the perineum. Trace this neurovasculature as it passes through the pudendal canal.

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)

Remove the skin of the urogenital triangle (N380 or TG6-25) from the labia majora laterally to the ischiopubic ramus. Dissecting through the fat of this triangle you will find the posterior labial nerve, artery, and vein. It may be easiest to trace this neurovasculature from the pudendal canal. Plate N413 or TG6-30 shows the pudendal nerve branching into the dorsal nerve of the clitoris (discussed later) and the perineal nerve. The perineal nerve will then have superficial and deep branches, which innervate the musculature of the perineum. In addition to this the superficial branch will continue on to give off posterior labial nerves. Similarly, the internal pudendal artery (N404 or TG6-29) will give off the perineal artery (the internal pudendal artery continues on and is still called the internal pudendal artery). The perineal artery will continue and give off the posterior labial artery (N404 or TG6-29).

Plates N379 or TG6-27, N395, and N404 identify the ischiocavernosus and bulbospongiosus muscles. Plate N379 or TG6-28 identifies the perineal body. Plate N379 or TG6-27 shows how the bulbospongiosus muscle lays on top of the vestibular bulb and ends at the base (shaft) of the clitoris). Reflect this muscle to reveal the vestibular bulb. Plate N413 or TG6-30 shows the deep branch of the perineal nerve giving off muscular branches. The greater vestibular glands are identified at the posterior margin of the vestibular bulbs in plate N379 or TG6-27. Next, reflect the ischiocavernosus muscle (N379 or TG6-27) to reveal the crus of the clitoris (N379). The shaft of the clitoris (N379 or TG6-08) is formed from two corpora cavernosa clitoridis (erectile bodies that underlie the ischiocavernosus muscle on both sides of the body). Plate N413 or TG6-30 shows the dorsal nerve of the clitoris (continuation of pudendal nerve after it gives off the perineal nerve) running deep to get to the dorsal side of the clitoris. Plate N404 or TG6-29 shows the dorsal arteries of the clitoris as a terminal branch of the internal pudendal artery. The deep dorsal vein of the clitoris takes a much different path than the artery (the path is shown in plates N265 or TG6-28 and N357). The glans clitoridis is identified in plate N377 or TG6-25. On one side cut the crus of the clitoris off of the ischiopubic ramus and free the vestibular bulb from the perineal membrane. Now you should be able to find two other major terminal branches of the internal pudendal artery: the deep artery of the clitoris (travels within the corpus cavernous clitoridis) and the artery to the bulb of the vestibule (see plate N404 or TG6-29 for these arteries). Plates N265 or TG6-28 and N357 or TG6-08 show the deep dorsal vein of the clitoris passing between the arcuate pubic ligament (N344 or TG6-24) and the perineal membrane. Plates N404 or TG6-29 and N413 or TG6-30 trace the dorsal artery and nerve of the clitoris respectively. Cutting through the corpus cavernous clitoridis and the vestibular bulb should reveal a tunica albuginea covering each. The tunica albuginea is not labeled in Netter's atlas on the female, but the male homologues of the corpus cavernosum clitoridis and the vestibular bulb (corpus cavernosum penis and corpus spongiosum penis) are shown covered with tunica albuginea in plate N381 or TG6-32.

Step 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)

Remove the skin from the penis, scrotum, and perineum (be careful because there is no underlying fat). Plates N380 or TG6-26, N382, and N387 or TG6-31 label the tunica dartos scroti. Plate N387 or TG6-31 shows the half scrotum removed (you need to pull it aside, not remove it) to reveal the ventral surface of the penis. Plate N411 or TG6-30 identifies the posterior scrotal nerve as the terminal branch of the superficial branch of the perineal nerve (the perineal nerve is formed when the pudendal nerve branches into perineal nerve and the dorsal nerve of the penis). Plate N405 or TG6-29 identifies the posterior scrotal artery as the terminal branch of the perineal artery (the perineal artery branches off the internal pudendal artery).

Plate N381 or TG6-27 labels the ischiocavernosus and bulbospongiosus muscles (the fascia of these muscles completely invests the shaft of the penis. Plates N381 and N382 or TG6-27 show the ischiocavernosus muscle overlying the crus of the corpus cavernosum and the bulbospongiosus muscle overlying the bulb of the corpus spongiosum (also see plate N385 or TG6-31). Reflect one ischiocavernosus muscle and reflect the bulbospongiosus muscle to reveal the corpus spongiosum and cavernosum. Plate N411 or TG6-30 shows muscular branches coming from the deep branch of the perineal nerve. Plates N382 and N385 or TG6-27 identify the corpus cavernosum, corpus spongiosum, glans, and shaft of the penis. Plate N405 or TG6-31A and TG6-31B shows the dorsal artery of the penis (also in plate N381 or TG6-32). Plate N411 or TG6-30 shows the dorsal nerve of the penis. The deep dorsal vein takes a different path than the dorsal artery of the penis. This vein is labeled in plates N265 or TG6-31, N359 or TG6-28, N405, and N404. Next, on one side only, cut a cross section through the penis. Plate N381 or TG6-32 labels the tunica albuginea surrounding both the corpus cavernosum and the corpus spongiosum. It also labels the deep artery of the penis traveling within the corpus cavernosum. The source of the deep artery of the penis is the internal pudendal artery (N405 or TG6-31). Next, cut the crus of the penis away from the ischiopubic ramus (on one side) and free the bulb of the penis from its attachment to the perineal membrane (see plate N382 or TG6-27). This should allow you to find two important branches of the internal pudendal artery: the deep artery of the penis and the artery to the bulb (see plate N405 or TG6-28). Plate N385 or TG6-09 labels the penile (spongy) urethra, bulb of the penis, and the navicular fossa. Plate N364 or TG6-32 labels the deep dorsal vein, dorsal arteries, and superficial dorsal vein of the penis. The deep dorsal vein passes between the arcuate pubic ligament and the anterior border of the perineal membrane (N265 or TG6-31B, N359 or TG6-28, N383 or TG6-31A, and N405). The dorsal artery of the penis is a branch off of the internal pudendal artery (see plate N405 or TG6-31B). The superficial dorsal vein of the penis is a tributary to the external pudendal veins (N265 or TG5-02).

Plates N379 or TG6-28, N381 or TG6-27, N404, and N405 show the perineal membrane in the male. Plate N365 or TG6-09, N379, and N362 or TG6-10 show the female urethra (all of it is considered membranous) and the female sphincter urethrae muscle. Plate N385 or TG6-28 shows the bulbourethral (Cowper's) gland embedded in the sphincter urethrae in the male. Plate N385 or TG6-09 also reviews the male urethra (membranous, prostatic, and penile/spongy portions). Plates N407 or TG6-33, TG6-34 and N266 or TG5-37 review the lymphatics of the pelvis and perineum.