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The perineum lies below the pelvic diaphragm. It forms a diamond-
to the vagina is from the vaginal artery (branch of the internal iliac
shaped area when viewed from below that can be divided into an anter-
artery) and the vaginal branch of the uterine artery.
ior urogenital region and a posterior anal region by a line joining the
ischial tuberosities horizontally. lower vagina drains to the superficial inguinal nodes. The blood supply
(b) In the male (Fig. 25.1)
Anal region (Figs 25.1 and 17.2) The external urethral sphincter (striated muscle) lies deep to the per-
The anal region contains the anal canal and ischiorectal fossae. ineal membrane within a fascial capsule termed the deep perineal
• Anal canal: is described earlier (p. 43). pouch. In addition to the sphincter, two glands of Cowper are also
• Anal sphincter: comprises external and internal sphincter compon- contained within the deep pouch. The ducts from these glands pass
ents. The internal anal sphincter is a continuation of the inner circular forwards to drain into the bulbous urethra. Inferior to the perineal mem-
smooth muscle of the rectum. The external anal sphincter is a skeletal brane is the superficial perineal pouch which contains the:
muscular tube which, at its rectal end, blends with puborectalis to form • Superficial transverse perineal muscles: run from the perineal
an area of palpable thickening termed the anorectal ring. The compet- body to the ischial ramus.
ence of the latter is fundamental to anal continence. • Bulbo-spongiosus muscle: covers the corpus spongiosum. The lat-
• Ischiorectal fossae: lie on either side of the anal canal. The medial ter structure covers the spongy urethra.
and lateral walls of the ischiorectal fossa are the levator ani and anal • Ischio-cavernosus muscle: arises on each side from the ischial
canal and the obturator internus, respectively. The fossae are filled with ramus to cover the corpus cavernosum. It is the engorgement of venous
fat. The anococcygeal body separates the fossae posteriorly; however, sinuses within these cavernosa that generate and maintain an erection.
infection in one fossa can spread anteriorly to the contralateral fossa Hence, the penile root comprises a well-vascularized bulb and two
forming a horseshoe abscess. The pudendal (Alcock’s) canal is a sheath crura which are supplied by branches of the internal pudendal artery.
in the lateral wall of the ischiorectal fossa. It conveys the pudendal The erectile penile tissue is enclosed within a tubular fascial sheath. At
nerve and internal pudendal vessels from the lesser sciatic notch to the the distal end of the penis the corpus spongiosum expands to form the
deep perineal pouch (see below). The inferior rectal branches of the glans penis. On the tip of the glans the urethra opens as the external
pudendal nerve and internal pudendal vessels course transversely urethral meatus. The foreskin is attached to the glans below the meatus
across the fossa to reach the anus. by a fold of skinathe frenulum.

Urogenital region The scrotum
The urogenital region is triangular in shape. The perineal membrane is The skin of the scrotum is thin, rugose and contains many sebaceous
a strong fascial layer that is attached to the sides of the urogenital tri- glands. A longitudinal median raphe is visible in the midline. Beneath the
angle. In the male it is pierced by the urethra and, in females, by the skin lies a thin layer of involuntary dartos muscle. The terminal spermatic
urethra and vagina. cords, the testes and their epididymes are contained within the scrotum.
(a) In the female (Fig. 25.2) Testis and epididymis (Fig. 25.3)
• Vulva: is the term given to the female external genitalia. The mons The testes are responsible for spermatogenesis. Their descent to an extra-
pubis is the fatty protuberance overlying the pubic symphysis and abdominal position favours optimal spermatogenesis as the ambient
pubic bones. The labia majora are fatty hair-bearing lips that extend scrotal temperature is approximately 3°C lower than body temperature.
posteriorly from the mons. The labia minora lie internal to the labia • Structure: the testis is divided internally by a series of septa into
majora and unite posteriorly at the fourchette. Anteriorly, the labia approximately 200 lobules. Each lobule contains 1–3 seminiferous
minora form the prepuce and split to enclose the clitoris. The clitoris tubules which anastomose into a plexus termed the rete testis. Each
corresponds to the penis in the male. It has a similar structure in that it is tubule is coiled when in situ, but when extended measures approxim-
made up of three masses of erectile tissue: the bulb (corresponding to ately 60 cm. Efferent ducts connect the rete testis to the epididymal
the penile bulb) and right and left crura covered by similar but smaller head. They serve to transmit sperm from the testicle to the epididymis.
muscles than those in the male. As in the male, these form the contents • The tunica vaginalis, derived from the peritoneum, is a double
of the superficial perineal pouch. The deep perineal pouch, however, covering into which the testis is invaginated.
contains the vagina as well as part of the urethra and sphincter urethrae • The tunica albuginea is a tough fibrous capsule that covers the testis.
and internal pudendal vessels. The vestibule is the area enclosed by the • The epididymis lies along the posterolateral and superior borders of
labia minora and contains the urethral and vaginal orifices. Deep to the the testicle. The tunica vaginalis covers the epididymis with the
posterior aspect of the labia majoris lie Bartholin’s glandsaa pair of exception of the posterior border.
mucus-secreting glands that drain anteriorly. They are not palpable in • The upper poles of both the testis and epididymis bear an appendix
health but can become grossly inflamed when infected. testis and appendix epididymis (hydatid of Morgagni), respectively.
• Urethra: is short in the female (3–4 cm). This factor contributes • Blood supply: is from the testicular artery (a branch of the abdom-
towards the predisposition to urinary tract infection due to upward inal aorta, p. 32). Venous drainage from the testicle is to the pampini-
spread of bowel organisms. The urethra extends from the bladder neck form plexus of veins. The latter plexus lies within the spermatic cord
to the external meatus. The meatus lies between the clitoris and vagina. but coalesces to form a single vein at the internal ring. The left testicu-
• Vagina: measures approximately 8–12 cm in length. It is a muscular lar vein drains to the left renal vein whereas the right testicular vein
tube that passes upwards and backwards from the vaginal orifice. The drains directly to the inferior vena cava.
cervix projects into the upper anterior aspect of the vagina creating • Lymphatic drainage: is to the para-aortic lymph nodes.
fornices anteriorly, posteriorly and laterally. Lymph from the upper • Nerve supply: is from T10 sympathetic fibres via the renal and aortic
vagina drains into the internal and external iliac nodes. Lymph from the plexuses.
The perineum 59