Chapter 9:  Pelvis

The bony pelvis is formed by the right os coxa , anteriorly and laterally on the right, the left os coxa , anteriorly and laterally on the left and the sacrum   and coccyx , dorsally between the two os coxae.

Refer to individual human bones and study the bony landmarks. On the os coxa  locate the ilium , ischium , and pubis . Observe that they meet at the acetabulum . Identify  on the ischium the tuberosity , lesser sciatic notch , and spine ; on the pubis, the pubic crest , tubercle and symphyseal surface ; on the ilium, the fossa , crest , tubercle  , anterior superior spine , anterior inferior spine , posterior superior spine , posterior inferior spine , and auricular surface . The greater sciatic notch is formed by the ilium and the ischium.

Identify on the sacrum the promontory , sacral canal , anterior sacral foramina and posterior sacral foramina . Observe the three to five rudimentary vertebrae of the coccyx.

Refer to an articulated human pelvis and study the bony landmarks. Identify  the pelvic brim (pelvic inlet) , iliopectineal line , sacroiliac articulation , obturator foramen , acetabulum , symphysis pubis , pubic angle and pelvic outlet . Compare the male and female pelvis. Identify  the traits which distinguish one from the other.

Examine the female genital system.  Identify the body of the uterus  dorsal to the urinary bladder. Trace the paired uterine horns  cranially from the body of the uterus to the smaller uterine tubes (oviducts) . The uterine tube courses first cranially, lateral to the ovary and then caudally. The distal end of the uterine tube forms a funnel-like infundibulum  . The oval-shaped ovaries  lie just caudal to the kidneys.

Examine the broad ligaments (peritoneum), supporting the ovaries, uterine tubes and uterus . The mesovarium extends from the dorsal body wall to the ovary, the mesosalpinx extends between the uterine tube and the dorsal body wall, and the mesometrium extends between the uterus and the dorsal body wall of the lumbar and pelvis region.

Identify the suspensory ligament of the ovary containing the ovarium artery and vein. It is the most lateral part of the cranial border of the broad ligament.  The round ligament   of the uterus extends along the mesometrium from the cranial end of the uterine horn to the internal inguinal ring.

Remove the skin from the pubic region and with a scalpel make a midventral incision through the muscles to the pubic symphysis. Continue the incision through the midventral symphysis.  Bend both thighs dorsally as far as possible. Carefully dissect the fat and fascia away from the pelvic diaphragm   which attaches the vagina and the rectum to the pelvic outlet.

Identify the vagina   caudal to the body of the uterus and trace it caudally through the pelvic canal. Trace the urethra caudally to its union with the vagina. The vagina is continuous caudally with the vestibule  , which extends from the vagina to the outside.  Incise around the opening of the vestibule and separate the vestibule and vagina from the rectum. Make a longitudinal incision through the lateral wall of the vestibule, vagina and body of the uterus. Identify the opening of the urethra   in the ventral wall between the vestibule and vagina. Note that the wall of the vestibule is smooth and that of the vagina contains longitudinal ridges, rugae  . The cervix is the junction between the vagina and the uterus.

Examine the male genital system. Make a midventral incision through the skin of the pubic region and reflect the skin laterally. Clean the fat and identify the spermatic cords and their covering, the spermatic fascia, as they pass superficially ventrolateral to the pelvic symphysis. Trace and identify each spermatic cord with its spermatic fascia caudally to the scrotum. Make a vertical incision in the right scrotum and remove  and observe the fascial sac , which lies at the caudal end of the spermatic fascia within the scrotum. Remove the left fascial sac.

Make a longitudinal incision in the right fascial sac. Remove and observe the large, round testis . Extend the incision cranially along the spermatic fascia to the abdominal wall. Observe the ductus deferens (vas deferens) which is accompanied by the internal testicular arteries and veins within the spermatic fascia.

Trace the ductus deferens caudally to the tail of the epididymis .  Identify the tail of the epididymis on the caudal end of the testis, the body of the epididymis on the dorsal surface of the testis, and the head of the epididymis on the craniolateral surface of the testis. The tunica albuginea encapsulates the testis and the epididymis.

On the bull testis, Identify the tunica vaginalis (fascial sac) and the cremaster muscle in the spermatic fascia. Open the fascial sac and the spermatic fascia.  Identify the epididymis (head , body and tail ) on the testis and the vas deferens originating from the tail of the epididymis and passing cranially through the spermatic fascia.  Make a midsagittal section of the testis through the epididymis. Identify the seminiferous tubules , which make up the mass of the testis and the tunica albuginea , which surrounds the seminiferous tubules.

With a scalpel make a midventral incision through the muscles to the pubic symphysis. Continue the incision through the midventral symphysis.  Bend both thighs dorsally as far as possible.  Carefully dissect the fat and fascia away from the pelvic diaphragm (note that these are pictures of a female's pelvic diaphragm, but the male's would be in the same location and look essentially the same), which attach the penis and the rectum at the pelvic outlet.

Trace the ductus deferens cranially through the inguinal canal.  It courses medially and loops around the ureter and courses caudally to enter the dorsal aspect of the prostatic urethra.  Identify the prostate at the point of entrance of the ductus deferens.

Examine the root of the penis caudal to the urethra.  It consists of a single bulb and two crura.  The bulb lies dorsomedial to the crura.  The crura are attached laterally to the ramus of the ischium by the ischiocavernosus muscle.  Transect the crura from their attachment to the ischium and observe the cylindrical erectile tissue.

Identify the penis from the rectum and identify the paired bulbourethral glands on the dorsolateral aspect of the distal end of the membranous urethra. The body of the penis extends distally from the root of the penis to the glans penis .  The glans penis is surrounded by a sheath of skin, the prepuce.  Remove the skin and observe the enlarged glans penis and its spines.

Displace the rectum and urinary bladder to the right. Clean the arteries lateral and dorsal to the rectum.  Observe the external iliac arteries   as they arise from the aorta and course to the lower limbs.

Identify the internal iliac arteries   as they arise from the terminal portion of the aorta.  Trace them caudally to the pelvic cavity and identify their branches.  The cranial vesicle (umbilical) artery  is the first branch of the internal iliac artery.  It courses ventrolaterally to the urinary bladder.

The cranial gluteal artery  arises from the internal iliac artery caudal to the vesicle artery, deep within the pelvic cavity.  It courses dorsolaterally over the greater sciatic (ischiatic) notch to the gluteal muscles.  The caudal gluteal artery  arises from the internal iliac artery caudal to the cranial gluteal artery and courses dorsolaterally over the lesser sciatic notch to the gluteal region.  It is accompanied by the lumbosacral cord.

The internal pudendal artery (middle hemorrhoidal)  is the terminal branch of the internal iliac artery.  It courses ventrally and then caudally along the lateral surface of the rectum.  The aorta continues caudally as the medial sacral artery  , which courses along the ventral aspect of the tail.  The left and right common iliac veins join to form the caudal vena cava .

Identify the obturator nerve  medial to the psoas minor muscle, as it passes caudally along the lateral wall of the pelvis, dorsomedial to the common iliac vein.  It passes through the obturator foramen .

Identify the lumbosacral cord (trunk)   caudal to the origin of the obturator nerve and dorsal to the internal iliac artery and vein.  The lumbosacral cord and the first sacral nerve join to form the sciatic (ischiatic) nerve to the lateral surface of the thigh.