PELVISPerineum
- The external anal sphincter,innervated by the pudendal nerve, pro-
vides the brief voluntary contraction necessary to counter the passage of
a peristaltic wave. - The rectal submucosal venous plexusforms anastomotic connections
between the middle rectal veins that drain directly into the internal iliac
veins and the superior rectal veins that drain into the hepatic portal sys-
tem. This is a site for varices (hemorrhoids). - The internal pudendal arteriesare the sole vascular supply of both
male and female erectile tissue. - The deep dorsal veinprovides venous return from the penis or clitoris
by passing through the urogenital diaphragm and draining into the pro-
static or vesicle venous plexus, respectively. - The cremaster muscleof the spermatic cord is innervated by the genital
branch of the genitofemoral nerve. This provides the efferent limb for
the cremaster reflex (L1–L2), the elevation of the testes within the scro-
tum when the inner thigh is scratched. - The cavity of tunica vaginalisis a potential space that represents the
detached portion of the peritoneal cavity that surrounds the testis except
posteriorly. The testis is “retroperitoneal” even in the scrotum. - Because the superficial perineal space is limited by superficial fascial
attachment to the deep transverse perineal muscle, extravasations of
blood or urine will not pass into the anal triangle. - The superficialperinealspace contains “sexuallypleasurablestructures”
(thanks to Dr. L. Wetzel. M.D.) and is superficial to the perineal mem-
brane and limited by Scarpa’s and Colles’ superficial fascia in females and
Scarpa’s, dartos and Colles’ superficial fascia in males. Scarpa’s superfi-
cial fascials attached to deep investing fascia of external oblique and rec-
tus abdominis half way up to the umbilicus and laterally at the inguinal
ligament. Colles’ superficial fascials attached to ischiopubic ramus and
inferior edge of perineal membrane.
High-Yield Facts 57