Carnivore Pelvic Cavity and Reproductive Vasculature

Iliac arteries and Branches

The paired iliac arteries supply the pelvis and pelvic limb. The external iliac arteries run ventrocaudally and are bilateral.  Each becomes the femoral artery as it leaves the abdomen through the vascular lacuna (recall that the name-change from external iliac a. to femoral a. is the vascular lacuna.) The internal iliac arteries arise caudal to the external iliac and pass caudolaterally into the pelvis. The left and right internal iliac arteries and the smaller, unpaired median sacral artery terminate the aorta.

The deep femoral artery is the only branch of the external iliac artery and arises inside the abdomen near the vascular lacuna and courses caudally.  Once the external iliac artery exits the vascular lacuna its name changes to the femoral artery.

Typically in the dog, two vessels leave the ventral surface of the deep femoral artery within the abdomen by a short pudendoepigastric trunk. These are the external pudendal and caudal epigastric arteries. In the cat, there is usually no pudendoepigastric trunk; the caudal epigastric a. and external pudendal a. each arise separately from the deep femoral a.  Sometimes, this is the case in the canine as well, and at times, the dog will not possess a PE trunk.  The external pudendal artery passes through the inguinal canal.  Once it exits the inguinal canal, it gives rise to the superficial caudal epigastric artery, which itself courses over the superficial inguinal lymph node.

The superficial caudal epigastric artery primarily supplies the skin and mammary glands in the caudal abdominal region. Additionally, in males, it gives off small branches to the preputial skin.

The superficial inguinal lymph nodes primarily drain the skin of the lower abdomen, inguinal area, perineum, and the external genitalia (scrotum or vulva), as well as the caudal mammary glands. They also receive lymphatic drainage from the pelvic limb, specifically from areas distal to the stifle joint.  They drain to the medial iliac lymph nodes.

The caudal epigastric artery arises from the pudendoepigastric trunk and passes cranially on the dorsal surface of the rectus abdominis. It supplies the caudal half of the rectus abdominis and the ventral parts of the oblique and transverse muscles.

In the carnivore, the internal iliac artery gives off the rudimentary umbilical artery (in the adult, the round ligament of the bladder) and terminates cranial to the sacroiliac joint as the caudal gluteal and internal pudendal arteries.  In the fetus, the umbilical artery is a large, paired vessel that carries blood from the aorta to the placenta through the umbilicus.  The remnant of this vessel, the round ligament of the bladder, runs along the free edge of the lateral ligament of the bladder. It arises near the origin of the internal iliac artery and courses to the apex of the bladder in its lateral ligament. FYI:  In some specimens it remains patent this far and supplies the bladder with cranial vesical arteries. Distal to the bladder the vessel is obliterated. There are no visible remnants in the median ligament of the bladder, which, you will recall, is the connecting peritoneum of the urachus in utero.  If the umbilical artery does remain patent, the caudal vesical arteries supply the entire bladder.

Note that the name change from internal iliac a. to the internal pudendal a. is the caudal gluteal a. In the dog, the caudal gluteal a. arises after a relatively short distance caudal to where umbilical artery branches.

In the cat, the first artery to branch from the internal iliac artery after the umbilical artery is the cranial gluteal artery.   In the cat, the cranial gluteal artery branches independently from the internal iliac artery. The caudal gluteal a. does not branch from the internal iliac a. until much farther caudally than it does in the dog. Therefore, the internal iliac a. is short in the dog and long in the cat; the internal pudendal a. is long in the dog and short in the cat.  See diagrams to better visualize these species differences.

The ovarian artery of the female is homologous to the testicular artery of the male. These paired vessels arise from the aorta about halfway between the renal and external iliac arteries. The ovarian artery varies in size, position, and tortuosity, depending on the degree of development of the uterus. Each ovarian artery divides into two or more branches in the mesovarium just medial to the ovaries. Branches supply the ovary and its bursa and the uterine tube and horn. The branch to the uterine horn anastomoses with the uterine artery, a branch of the vaginal artery that runs cranially in the mesometrium.

The ovarian artery and vein along with surrounding intra-abdominal fat form together form the ovarian pedicle, which is a clinical term.  The ovarian pedicles must be isolated and ligated in order to perform an ovariohysterectomy (spay).

The testicular artery leaves the aorta in the midlumbar region and crosses the ventral surface of the ureter. Recall that the testicular artery, vein, and nerve plexus lie in a peritoneal fold, the mesorchium, which can be followed to the level of the vaginal ring, through the inguinal canal and into the scrotum.

The right testicular and ovarian veins enter the caudal vena cava near the origin of the artery from the aorta. However, the left testicular and ovarian veins usually enter the left renal vein. This is important surgically.

The internal pudendal artery passes obliquely across the greater ischiatic notch. It continues along the dorsal border of the ischiatic spine lateral to the coccygeus muscle and medial to the gluteal muscles and sacrotuberous ligament in the dog.  Rather than passing lateral to the coccygeus and levator ani mm, as in most species, the internal pudendal a of the cat travels medial to these mm and near the lateral surface of the rectum.

The internal pudendal artery terminates as a ventral perineal artery, a variable urethral artery, and an artery of the penis or clitoris.  The ventral perineal artery may be seen passing caudally. It supplies the caudal rectal artery to the rectum and anus and terminates in the skin of the perineum and the scrotum or vulva.

Note regarding variation in the vasculature at this point: Alternatively, the caudal rectal a. may branch from the internal pudendal a. proximal to and independently from the ventral perineal a. OR the caudal rectal a. may give rise to the ventral perineal a. However these branches arise from the internal pudendal artery, as always, name them for where they are going (not branching patterns). The name change from internal pudendal a. to artery of the penis/clitoris occurs when BOTH the ventral perineal and caudal rectal aa. have branched from the internal pudendal a, in whatever pattern such may occur.

The artery of the penis courses caudoventrally and terminates at the level of the ischial arch as three branches: deep artery of the penis (into corpus cavernosum), artery of the bulb of the penis (into the bulb), and dorsal artery of the penis (not surprisingly, along the dorsal aspect of the penis). In the female the artery of the clitoris courses caudoventrally to supply the clitoris and vestibular bulb.

Nerves of the Carnivore Pelvic Cavity

The pelvic plexus lies caudal to a transverse plane passing through the pelvic inlet and dorsal to the prostate. It is closely applied to the surface of the rectum and the vaginal/prostatic artery. It can be identified by tracing the left hypogastric nerve to it. Recall that the left and right hypogastric nerves originate in the caudal mesenteric ganglion and provide sympathetic innervation to the pelvic cavity.  Occasionally, ganglia are large enough to be recognized in the plexus. The pelvic plexus contains sympathetic fibers from the hypogastric nerve and parasympathetic fibers from the pelvic nerve.

The pelvic nerve is formed by parasympathetic preganglionic axons that leave the ventral branches of the three sacral spinal nerves. The pelvic plexus ganglia contain the cell bodies of post-ganglionic parasympathetic nerves which ultimately innervate the pelvic viscera. It supplies branches to the urogenital organs, the rectum, and the descending colon. The branches to the urogenital organs join the pelvic plexus and follow the vaginal/prostatic vessels to these organs.  The pelvic nerve will extend dorsally from it, parallel to the prostatic/vaginal artery.

The pudendal nerve arises from all three sacral nerves and provides somatic/voluntary innervation to the pelvic cavity and perineum. It passes caudolaterally, where it lies lateral to the levator ani and coccygeus muscles, medial to the superficial gluteal muscle, and dorsal to the internal pudendal vessels. It appears superficially in the ischiorectal fossa after emerging from the medial side of the superficial gluteal muscle and courses caudomedially toward the pelvic symphysis at the ischial arch.

a. The caudal rectal nerve may arise from sacral nerves or may leave the pudendal nerve at the caudal border of the levator ani muscle. It innervates the external anal sphincter.

b. The perineal nerves arise from the dorsal surface of the pudendal nerve. They supply the skin of the anus and the perineum and continue to the scrotum or labium. Short nerves from the pudendal or perineal nerves supply the muscles of the penis or the vestibule and vulva.

c. The dorsal nerve of the penis in the male (or of the clitoris in the female) curves around the ischial arch and reaches the dorsal surface of the penis, where it courses cranially. It continues through the glans penis and ends in the skin covering the apex of the penis. It provides sensory nerves to the skin of the glans. In the female the smaller dorsal nerve of the clitoris runs ventrally to the ventral commissure of the vulva, where it terminates in the clitoris.

Clinical Application:  Anal Sac Resection/Perineal Hernia

    When performing an anal sac resection or a perineal hernia repair, it is imperative to recognize that the innervation to the external anal sphincter, the caudal rectal n., needs to be avoided.  Injury to the nerve can cause fecal incontinence as it provides conscious control over the external anal sphincter m.

Ungulate Pelvic Cavity and Reproductive Vasculature

Lymph nodes and Aortic termination

Numerous lymph nodes are associated with the terminal part of the abdominal aorta. Those located along the aorta, caudal to the kidneys, are designated lumbar aortic nodes.

External iliac a. and its branches

Ungulate Pelvic Vessels and Innervation

Innervation

The pudendal nerve arises rom various sacral nerves  in the ungulate (S2-S4 in ruminants; S2/3-S4 in the horse) and courses caudoventrally on the medial surface of the sacrosciatic ligament, where it can be palpated rectally in the ox.  Note that the pudendal nerve is more invested in the sacrosciatic ligament in the horse and we see a portion of it from the lateral side.  Of note is that that external anal sphincter m. is provided somatic innervation by the caudal rectal nerve, which is NOT a branch of the pudendal nerve in the ungulate.  The pudendal nerve supplies sensory innervation to the rectum, perineal skin, and internal and external reproductive organs and motor to much of the striated perineal musculature.  Deep and superficial perineal nerves in addition to various cutaneous branches originate from the pudendal nerve, which finally continues as the dorsal nerve of the penis/clitoris.  The dorsal nerve of the penis supplies innervation to the following structures:  the skin and fascia of the penis, including the prepuce, and to the glans penis. The dorsal nerve of the penis also innervates the following structures:

• Penile shaft: The dorsal nerve of the penis provides sensory innervation to the skin of the penile shaft.
• Glans penis: It also innervates the glans penis, contributing to its sensory function and the reflex ejaculatory activity. 
• Anterior urethra: The dorsal nerve has fibers that extend into the corpus spongiosum to innervate the urethral lumen, relaying sensory information during micturition (urination) and ejaculation.

The pelvic nerve lies medial to the pudendal nerve and adjacent to the vaginal/prostatic aa. and carries preganglionic parasympathetic fibers from the sacral segments of the spinal cord to the pelvic plexus, from which they are distributed to the pelvic viscera.  Note that unlike in the thorax and abdomen, the pelvic ganglion contains nerve cell bodies of post-ganglionic parasympathetic nerves.  Recall that in the head, thorax, and abdomen, ganglions contain nerve cell bodies of post-ganglion sympathetic nerves.

Recall that the pelvic plexus also receives the hypogastric nn. which supply sympathetic innervation to the pelvic viscera.

The udder of the cow is supplied by sensory and autonomic nerves. The sensory innervation is derived from the ventral cutaneous branches of L1 and L2, the genitofemoral nerve (L3 and L4), and the mammary (superficial perineal) branch of the pudendal nerve. Of these, the genitofemoral nerve is of major importance, because it innervates much of the skin, the teats, and most of the glandular tissue.

The autonomic innervation is supplied by sympathetic fibers from the caudal mesenteric ganglion, which accompany the genitofemoral nerve through the inguinal canal.

Ungulate Pelvic Cavity and Reproductive Vasculature

In the mare, the uterine artery is a branch of the external iliac artery. In ruminants and the pig, the uterine artery typically arises as the first branch of the umbilical artery, which is a branch of the internal iliac artery.

The vaginal/prostatic artery (which supply their namesakes) and then the caudal rectal artery (supplies the external anal sphincter muscle) and the ventral perineal a. (supplies, you guessed it, the ventral perineum) branch from the internal pudendal a. distal to the origin of the caudal gluteal artery.

Once they have branched, the internal pudendal artery changes name to the artery of the penis/clitoris.   The artery of the penis then splits into the dorsal artery of the penis, artery of the bulb, and deep artery of the penis.

Recall that the the stallion has developed an extensive external pudendal venous plexus to receive blood from the cavernous spaces of the penis immediately following dismounting. The venous plexus is drained by the large accessory external pudendal vein, which does not return through the inguinal canal but rather perforates the origin of the gracilis muscle and joins the deep femoral vein.  The much smaller external pudendal vein enters the abdominal cavity through the inguinal canal, along side the external pudendal artery, as is typical.

Superficial Inguinal (Mammary) Lymph Node

Numerous large, superficial lymphatics drain the mammary tissue to the mammary ln. (superficial inguinal ln.).
Efferent lymphatics in the cow (and goat?) then continue through the inguinal canal, to the external iliac ln.(and in the mare to the proximal femoral ln.).

The superficial lymphatics of the cow udder can be observed in the living animal, and their direction is primarily caudodorsal. These lymphatics can be distinguished from the superficial veins, which course in a more
craniodorsal direction.