Part 4: Male Genitalia

In the MALE specimens, identify the scrotum. Incise the skin of the scrotum and peel the skin off of the testes. (See DG Fig. 4-6)

• Comment: Note that just deep to the skin of the scrotum there is a cutaneous muscle, the tunica dartos. Contraction of this smooth muscle is responsible for bringing the testes closer or further away from the body in response to a cool or warm environmental temperature, respectively. (This is necessary because sperm formation is optimized at specific temperatures.) (See DG Fig. 4-7C)

  Related Learning Objective

  • D6.4

   

Identify one testis (right or left) and observe the spermatic cord attached to it. The spermatic cord is composed of the ductus deferens and the testicular a. & v. (See DG Figs. 2-80, and 4-6)

• Comment: You should note that spermatic fascia surrounds the testis and the structures emerging from the superficial inguinal ring (but you need not identify it). (See DG Figs. 4-5, and 4-7C)

Observe the spermatic cord and identify the cremaster muscle coursing alongside/attaching to it (ID in dog; usually absent in cats – also identified in Chapter 3). Recall that the cremaster m. arises from the caudal edge of the internal abdominal oblique m. (See DG Figs. 2-80, 4-6, and 4-7, A, B & C)

• Reflect the spermatic fascia to identify the vaginal tunics which include a parietal and visceral component. (See DG Figs. 4-5, and 4-7, B & C)

  • • The parietal vaginal tunic is the outer layer (lining the ‘walls’ of the vaginal cavity). (See DG Figs. 4-5, and 4-7, B & C) Incise the parietal vaginal tunic over the spermatic cord and testis to see the vaginal cavity and the visceral vaginal tunic. (See DG Figs. 4-5, and 4-7C)

    • The visceral vaginal tunic is closely fused to the testis and epididymis and surrounds the ductus deferens.

    • The vaginal cavity is the ‘space’ you entered by incising the parietal vaginal tunic and is a continuation of the peritoneal cavity.

    • Comment: The mesorchium and mesoductus deferens are connecting mesenteries of the testis and ductus deferens. (These connecting mesenteries are continuous with the parietal and visceral vaginal tunics.) These will be covered in more detail in the Application portion of the course. (See DG Figs. 2-80, and 4-5)

      Related Learning Objective

      • D6.4

       

Identify the ductus deferens (a component of the spermatic cord). The ductus deferens is the ‘tube’ that carries sperm from the epididymis to the urethra. It is continuous with the tail of the epididymis at the caudal end of the testis. It is accompanied by the (small) deferent artery and vein. (See DG Figs. 2-80, 4-5, and 4-7, B & C)

Identify the testicular artery and vein (also components of the spermatic cord) attached to the cranial end of the testis. (See DG Figs. 2-80, and 4-5)

• Note that the testicular artery follows a tortuous path, weaving back and forth on its way to the testicle.

• Also note that along its course, the testicular v. forms a plexus of many branches that weaves around the testicular a.; identify this interwoven area of the vein known as the pampiniform (venous) plexus. This area usually appears very dark in color. (See DG Fig. 4-7, A & B)

Identify the epididymis associated with the testis. The epididymis has 3 parts: head, body, and tail. Note that the epididymis is found mostly on the lateral side of the testis. (See DG Figs. 2-80, 4-5, 4-6, and 4-7, A & C)

• Identify the head, body, and tail of the epididymis. (See DG Figs. 2-80, and 4-7A)

  • • The head of the epididymis is the cranial part where the epididymis communicates with the testis.

    • The body of the epididymis is the middle part.

    • The tail of the epididymis is the caudal part which is then continuous with the ductus deferens on the medial side of the testis.

      • • Dissection Note: The tail of the epididymis is attached to the vaginal tunic and spermatic fascia by the ligament of the tail of the epididymis and the tail of the epididymis is attached to the testis itself by the proper ligament of the testis. Identify the ligament of the tail of the epididymis on your specimen. (See DG Fig. 4-7B)

Moving inside the abdominal cavity, looking caudoventrally into the peritoneal cavity, observe the region of the vaginal ring and identify the deep inguinal ring. (See DgG Figs. 4-5, 4-11, and 4-43)

• Dissection Note: The vaginal ring is the opening formed by the parietal peritoneum as it leaves the abdomen and enters the inguinal canal to form the vaginal tunic/process. An accumulation of some amount of fat usually surrounds the vaginal ring region.

• The vaginal ring marks the position of the deep inguinal ring, which is formed by the reflection of transversalis fascia outside the vaginal ring. The deep inguinal ring represents the entrance to the inguinal canal.

Look for and identify the ductus deferens inside the abdominal cavity before it passes through the inguinal canal. (The ductus deferens are seen entering the urethra at the level of the prostate gland, which will be discussed later in this section.) (See DG Figs. 4-9A, 4-11, and 4-43)

• Comment: Note that the ductus deferens is attached to the abdominal and pelvic walls by the mesoductus deferens.

Review the concept of the inguinal canal (which the external pudendal vessels and genitofemoral nerve pass through) that was previously discussed in Chapter 3; note that this canal is a ‘passageway’ and not a distinct ‘structure’.

• The inguinal canal is a ‘slit’ between the abdominal muscles that forms a very short, natural passageway through the abdominal wall. It extends from the deep inguinal ring (inside the abdomen) to the superficial inguinal ring (outside the abdominal wall) and allows passage of various structures. These structures include the external pudendal a. and v., genitofemoral nerve, vaginal tunics, and spermatic cord (male) or vaginal process (female). (See DG Figs. 2-80 and 4-5)

Re-identify the testicular arteries (male) (left & right) branching from the aorta, which were previously dissected in Chapter 5. Attempt to trace at least one of the testicular aa. to the region of the left or right vaginal ring. (Recall that we have already dissected and identified the testicular a. with the spermatic cord.)

• Dissection Note: The testicular arteries may be small and easily broken, so dissect with care. (See DG Figs. 4-27, 4-28, 4-29, and 4-31)

• As previously mentioned, you should note that testicular veins satellite these arteries.

  Related Learning Objective

  • D6.6

   

Re-identify the ureters (left and right) (previously identified in Chapter 5) and trace them to the urinary bladder. Within the pelvis, identify the urethra leaving the neck of the urinary bladder. Attempt to identify the striated urethral m. (urethralis m.) surrounding the pelvic urethra. Note that in the male, the urethralis m. will be seen surrounding the part of the pelvic urethra just caudal to the prostate. (Note that this urethralis m. may also be referred to as the external urethral sphincter.) (See DG Figs. 4-38 and 4-39)

• Make a mid-ventral incision through the wall of the urinary bladder and urethra (in male dogs this will include the prostate gland).

• Open the urinary bladder and observe the entrance of the ureters into the bladder; identify the trigone of the bladder. The trigone of the bladder is the dorsal triangular area located between the ureteral openings and the urethral exit from the bladder. (See DG Fig. 4-42B)

Identify the prostate gland. The prostate gland surrounds the neck of the bladder and the beginning of the urethra. (See DG Figs. 4-39, 4-41, A & B, and 4-42A) The ductus deferens are seen entering the urethra here (at the level of the prostate gland).

Re-identify the urethra and proceed to identify its parts (note that there is a slight difference for dog vs. cat) .

• In both the dog and cat, the urethra is composed of a pelvic part within the pelvis and a penile part within the penis. Identify these parts.

• In the DOG, the pelvic part of the urethra is made up of a prostatic part (running through the prostate) and a post-prostatic part (after the prostate). Identify these parts of the urethra in the dog specimens.

  • • Note that the post-prostatic part is covered by the urethralis m. (See DG Fig. 4-42A)

• In the CAT, the pelvic part of the urethra is made up of a long pre-prostatic part (before the prostate), a prostatic part (running through the prostate) and a post-prostatic part (after the prostate). Identify these parts of the urethra in the cat specimens.

  • • Note that the post-prostatic part is covered by the urethralis m.

Identify the prepuce. The prepuce is the sheath/fold of skin covering the glans of the penis. It has a smooth internal layer and a haired external layer. (See DG Figs. 4-6 and 4-41B)

• Comment: Note the fornix of the prepuce which is the point on the smooth internal layer of the prepuce where the skin reflects onto the glans of the penis.

• Identify the external opening of the prepuce, the preputial orifice.

• Open the prepuce with a mid-ventral incision and expose the penis. Continue the incision dorsally toward the anus to expose the entire length of the penis.

Identify the penis and its three regional parts: root, body & free part. (See DG Figs. 4-40 and 4-41, A & B)

• Dissection Note: In cats, the penis is quite short and directed caudally.

• The root of the penis is the proximal part formed by the left and right crura (anchored to the ischial arch) and the bulb of the penis. Where the crura come together on the midline of the penis marks the end of the root and beginning of the body.

  • • In the CAT specimen, caudal to the prostate, and immediately proximal to the root of the penis, identify the bulbourethral glands. (Dogs do not have these.)

• The body of the penis is the middle part, continuing from the root to the free part.

• The free part of the penis is the distal end (after the body) within the prepuce.

 Identify the retractor penis muscle, which is an elongated slip of mixed smooth and striated muscle fibers (so it will appear lighter in color than regular striated muscles). It originates from the ventral sacrum/first few caudal vertebrae and extends distally along the ventral surface of the penis to the glans of the free part. (See DG Fig. 4-47A)

• Dissection Note: In cats, with the penis being directed caudally, the retractor penis m. will appear ‘dorsally’ along the surface of the penis.

Examine the root of the penis and identify the crus (right and left; plural is crura). Recall that one crus was cut and reflected off of the pelvis when abducting the hind limb to open the pelvis and reveal the pelvic canal. Examine the cut crus and intact crus.

• Each crus (left and right) is made up of corpus cavernosum penis erectile tissue with a thick, white, fibrous tunic, the tunica albuginea, surrounding the erectile tissue.

  • • On the cut crus, identify the corpus cavernosum penis and the tunica albuginea. (See DG Fig. 4-50B)

      Related Learning Objective

      • D6.4

       

• Each crus (left and right) is then covered by a muscle, the ischiocavernosus m.

  • • Identify the ischiocavernosus m. covering the left and right crura. (See DG Figs. 4-47A and 4-50B)

Identify the bulbospongiosus muscle in between the ischiocavernosus muscles, ventral to the external anal sphincter, and running distally onto the body of the penis. (See DG Figs. 4-41B, 4-47, A & B, and 4-50)

• The bulbospongiosus m. covers the bulb of the penis. Identify the bulb of the penis between the crura (at the root of the penis). (See DG Figs. 4-47B and 4-50)

  • • The bulb of the penis is a dorsal, bilobed expansion of the corpus spongiosum penis erectile tissue which surrounds the urethra. (See DG Figs 4-41B and 4-50)

    • Make a transverse section through the root of the penis, similar to DG Fig. 4-50 letter A, to identify its parts. (Identify the corpus spongiosum penis on the cut surface.)

On the dorsal aspect of the body of the penis, use blunt dissection to identify the dorsal artery of the penis and the dorsal nerve of the penis. These will be discussed again later in this lab, but you should be aware of their location as you move on to the next step of the dissection of the penis.

Make 2 incomplete transections through the penis, one through the root and one through the body, to study the structures and components of the penis.

• Make the first (incomplete) transection through the root of the penis across both crura, similar to DG Fig. 4-50, letter B.

• Make the second (incomplete) transection through the body of the penis midway between the root and the free part, similar to DG Fig. 4-50, letter C.

Identify the region of the glans of the penis. (See DG Figs. 4-40, 4-41B, and 4-50)