Perineum

The pelvis consists of the bony pelvic girdle, the muscular and ligamentous pelvic floor, and the pelvic cavity, which contains viscera, vessels, and multiple nerves and muscles. The pelvic girdle, composed of 2 “hip” bones and the sacrum, is a ring-like bony structure of the axial skeleton that links the vertebral column with the lower extremities. The pelvic ring joints include the pubic symphysis anteriorly and the sacroiliac joints posteriorly. The hip bones are made up of 3 fused bones: the pubis, ischium, and ilium. The pelvic cavity houses various GI, urinary, and reproductive structures, which are supported by the muscles and connective tissue of the pelvic floor. The female pelvis, making accommodations for childbirth, is generally wider and larger than the male pelvis.

The testicles, also known as the testes or the male gonads, are a pair of egg-shaped glands suspended within the scrotum. The testicles have multiple layers: an outer tunica vaginalis, an intermediate tunica albuginea, and an innermost tunica vasculosa. The testicles are composed of testicular lobules (contain interstitial tissue) and seminiferous tubules (produce spermatozoa). Blood supply to the testicles is primarily provided by the testicular artery. Venous drainage is through testicular veins.

The rectum and anal canal are the most terminal parts of the lower GI tract/large intestine that form a functional unit and control defecation. Fecal incontinence can occur if this function is disturbed. Fecal continence is maintained by several important anatomic structures including rectal folds, anal valves, the sling-like puborectalis muscle, and internal and external anal sphincters. Peristaltic waves within the rectal muscularis, involuntary relaxation of the internal anal sphincter (controlled by the ANS), and voluntary relaxation of the external anal sphincter (controlled by the cerebral cortex) are essential for defecation to occur. The rich plexus of veins surrounding the anal canal can develop into hemorrhoids if dilated.

The vulva is the external genitalia of the female and includes the mons pubis, labia majora, labia minora, clitoris, vestibule, vestibular bulb, and greater vestibular glands. The vagina is the female genital canal, extending from the vulva externally to the cervix uteri internally. The structures have sexual, reproductive, and urinary functions and a rich blood supply, mainly arising from the internal iliac artery.

The penis is the male organ of copulation and micturition. The organ is composed of a root, body, and glans. The root is attached to the pubic bone by the crura penis, which are the extremities of the corpora cavernosa. The body consists of the 2 parallel corpora cavernosa and the corpus spongiosum, which sits beneath the corpora cavernosa and through which the urethra passes. The glans is ensheathed by the prepuce or foreskin. The penis is homologous with the clitoris in females.