Part 5: Terminal Aorta and Extensions of the Peritoneal Cavity

Return to the abdominal cavity, and looking dorsally, identify and trace the terminal branches of the descending abdominal aorta. The terminal branches of the aorta include the external iliac aa. (left and right), internal iliac aa. (left and right) and the median sacral a. (unpaired). (See DG Fig. 4-28) Use blunt dissection to trace these arteries as directed.

Identify the origins of the external iliac arteries (left and right) as they are given off of the aorta. These arteries run caudoventrally to supply the pelvis and pelvic limbs. (See DG Fig. 4-58)

• Each external iliac a. will then leave the abdomen through the vascular lacuna and become the femoral artery supplying each hind limb, which was previously dissected in Chapter 2. (See DG Figs. 4-55 and 4-58)

• Trace the external iliac a. caudoventrally and identify the deep femoral artery branching from it before it exits the abdomen through the vascular lacuna. (See DG Figs. 4-55, 4-58, and 4-60)

  • • Dissection Note: Note that the deep femoral a. branches from the external iliac INSIDE the abdomen, before the external iliac leaves the abdomen through the vascular lacuna to become the femoral a.

    • Trace the deep femoral a. caudally and identify the short pudendoepigastric trunk branching from it. (See DG Figs. 4-55 and 4-60)

    • Two branches are given off of the pudendoepigastric trunk, the external pudendal a. and the caudal epigastric a. (Note that these arteries were previously identified individually in Chapters 3 & 5, respectively. Now we are seeing where these two arteries originate from.)

      • • Identify the external pudendal a. leaving the pudendoepigastric trunk and passing through the inguinal canal. (See DG Figs. 2-79, 4-2, 4-33, and 4-60)

        • Identify the caudal epigastric a. leaving the pudendoepigastric trunk and coursing cranially on the deep surface of the rectus abdominis m. (See DG Figs. 4-33 and 4-60)

        • Dissection Note: In the CAT, note that the pudendoepigastric trunk gives off an additional branch within the abdominal cavity, the middle vesical artery, going to the bladder.

    • Dissection Note: The continuation of the deep femoral a. after it gives off the pudendoepigastric trunk is the medial circumflex femoral a. The medial circumflex femoral a. leaves the abdomen through the vascular lacuna and supplies the muscles of the medial thigh, but you need not identify if on your specimen. (See DG Figs. 4-55, 4-58, 4-60, 4-63, and 4-64) This continuation will be dissected on a demonstration animal for you to view.

      • • Comment: There are two branches of the medial circumflex femoral a., a deep branch and a transverse branch. These need not be dissected/identified.

Caudal to the external iliac arteries, identify the origins of the internal iliac arteries (left and right) as they are given off of the aorta. These arteries pass caudolaterally to supply the pelvis and pelvic limbs. (See DG Figs. 4-37, 4-55, and 4-58)

Identify the final branch from the aorta, the smaller, unpaired median sacral artery. This artery passes caudodorsally. (See DG Figs. 4-28, 4-38, 4-39, and 4-58)

On the side of the animal with the open pelvis, return to the internal iliac a. and carefully trace it to identify its main branches. The internal iliac a. will give off the umbilical artery and then terminates as the internal pudendal artery and caudal gluteal a. (See DG Figs. 4-37, 4-38, and 4-39)

• Important Note: The branching of the internal iliac artery varies considerably in the cat. Identify the arteries by the area they supply.

  • • Typically, in the cat, the internal iliac a. will give off an umbilical a. first, then a cranial gluteal a., and then terminates as the internal pudendal a. and caudal gluteal a. as described in the dog.

• Trace the internal iliac a. and identify the umbilical a. running to the apex of the urinary bladder. This artery arises near the origin of the internal pudendal a. (See DG Figs. 4-37, 4-38, and 4-39)

  • • Comment: The umbilical a. is a fetal remnant and is usually not patent in the adult animal. It will often look ‘nerve-like’ in appearance rather than like an artery.

• After the umbilical a. is given off, find the branching point of the internal iliac a. where it branches into the internal pudendal a. (coursing to pelvic viscera and external genitalia) and the caudal gluteal a. (coursing toward the pelvic wall to supply muscles outside of the pelvis and in the caudal thigh). (See DG Figs. 4-37, 4-38, and 4-39)

• The internal pudendal a. courses toward the pelvic viscera and gives off the vaginal a.(female)/prostatic a. (male). This branch leaves the internal pudendal a. at roughly a 45° angle and passes ventrally in an arch to give off several other branches. (See DG Figs. 4-37, 4-38, and 4-39)

  • • In FEMALES: The vaginal a. gives rise to the previously identified uterine a. The uterine a. courses cranially along the body and horn of the uterus in the broad ligament. (See DG Figs. 4-37 and 4-38)

    • In MALES: The prostatic a., gives rise to the artery of the ductus deferens. The artery of the ductus deferens tends to be quite small but will course alongside the ductus deferens which it supplies. (See DG Fig. 4-39)

    • Important Note: The branching of the internal pudendal a. varies considerably in the cat. Identify the arteries by the area they supply.

    • Comment: There are numerous other branches that will not be dissected, including the caudal vesical artery supplying the bladder and the middle rectal artery that courses caudally to supply the rectum and urethra, as well as the branches supplying the vagina (female) and prostate (male). (See DG Figs. 4-38 and 4-39)

• In the DOG specimens, the internal pudendal a. continues obliquely across the greater ischiatic notch (out of the pelvic cavity). The continuation of the internal pudendal a. passes lateral to the coccygeus m. and medial to the gluteal muscles (and sacrotuberous ligament), into the ischiorectal fossa. (Note that the artery is accompanied by the pudendal n.) In this region, the internal pudendal a. terminates as a ventral perineal a. (which gives off a caudal rectal a.) and an artery of the penis (male) or artery of the clitoris (female). (See DG Figs. 4-37, 4-38, 4-39, 4-40, and 4-68) In the CAT specimens, the internal pudendal a. continues caudally through the pelvic canal. (In the cat, the internal pudendal stays within the pelvic canal rather than passing out of the pelvis across the greater ischiatic notch as it does in the dog. The branching will also vary considerably.) In the cat, the internal pudendal a. will still terminate as a ventral perineal a. (which gives off a caudal rectal a.) and an artery of the penis (male) or artery of the clitoris (female).

  • • In the MALE, the artery of the penis terminates as three branches supplying the penis: artery of the bulb of the penis, deep artery of the penis, and dorsal artery of the penis. (See DG Figs. 4-39 and 4-40)

      • • Re-identify the dorsal artery of the penis running along the dorsal surface of the penis (previously identified during the male genitalia section).

        • Running alongside the dorsal artery of the penis, re-identify the dorsal nerve of the penis.

          • • Comment: The dorsal nerve of the penis is a branch from the pudendal n.

        • Dissection Note: In the cat, keep in mind that since the penis projects caudally, what would normally be the ‘dorsal aspect of the penis’ is located ventrally.

    • In the FEMALE, the artery of the clitoris may be small and difficult to find and need not be dissected; it supplies the clitoris and vestibular bulb. (See DG Figs. 4-37 and 4-38)

      Related Learning Objective

      • D6.3

       

Be familiar with the extensions of the peritoneal cavity (that extend into the pelvic region) and be sure to visualize them on your specimen. These extensions are the: pararectal fossa, rectogenital pouch, vesicogenital pouch, and pubovesical pouch. (See DG Figs. 4-8, 4-41, and 4-53)