Pelvis Anatomy Set 4

The lateral lobes on either side of the urethra form the major part of the prostate.

The free anterior borders of the levator ani are separated by a gap, the urogenital hiatus, through which the urethra (and, in the female, the vagina) passes.

The penis is composed of three cylindrical bodies of erectile cavernous tissue enclosed by a fibrous capsule, the tunica albuginea. Superficial to the capsule is the deep fascia of the penis (Buck’s fascia). Superficial to the deep fascia is the loose areolar tissue, which lies just beneath the skin of the penis. The tunica dartos is located in the scrotum.

The perineal body is the major structure incised during median episiotomy for childbirth.

Only the lower one-fifth to one-fourth of the vagina is somatic in terms of innervation. The innervation of this part of the vagina is from the deep perineal branch of the pudendal nerve.

When empty, the adult male or female urinary bladder is in the lesser pelvis, lying posterior and slightly superior to the pubic bones. It is separated from these bones by the potential retropubic space and lies inferior to the peritoneum, where it rests on the pelvic floor.

The lumen of the spongy urethra is approximately 5 mm in diameter: however, it is expanded in the bulb of the penis to form the intrabulbar fossa and in the glans penis to form the navicular fossa.

The pelvic splanchnic nerves contain parasympathetic fibers derived from S2, S3, and S4 spinal cord segments and visceral afferent fibers from cell bodies in the spinal ganglia of the corresponding spinal nerves.

Lithotripsy uses shock waves to break up a stone into small fragments that can be passed in the urine.

Urethral glands are present particularly in the superior part of the female urethra. The paraurethral glands are homologues to the prostate.

In its uppermost portion, at the base of the peritoneal broad ligament, the uterine artery runs transversely toward the cervix while the ureters pass immediately beneath them as they pass on each side of the cervix toward the bladder. This relationship (“water passing under the bridge”) is an especially important one for surgeons ligating the uterine artery, as in a hysterectomy.

The major part of the broad ligament, the mesentery of the uterus or mesometrium, is below the mesosalpinx and mesovarium.

The piriformis muscle leaves the lesser pelvis through the greater sciatic foramen to attach to the upper border of the greater trochanter of the femur.

The levator ani, a broad muscular sheet, is the largest and most important muscle in the pelvic floor.

The intermediate part of the urethra (membranous part) is the section passing through the external urethral sphincter and the perineal membrane. The short intermediate part, extending from the prostatic urethra to the spongy urethra, is the narrowest and least distensible part of the urethra.

The superior end of the vagina surrounds the cervix; the lower end passes anteroinferiorly through the pelvic floor to open in the vestibule.

The anterior aspect of the scrotum is supplied by anterior scrotal nerves derived from the ilioinguinal and the genital branch of the genitofemoral nerve. The posterior aspect of the scrotum is supplied by posterior scrotal nerves, provided by perineal branches of the pudendal and perineal branches of the posterior femoral cutaneous nerve.

The superior gluteal artery leaves the pelvis through the superior part of the greater sciatic foramen, superior to the piriformis muscle, to supply the gluteal muscles in the buttocks.

The puborectalis muscle unites with its partner to from a U-shaped sling around the anorectal junction. The puborectalis is responsible for the anorectal angle (perineal flexure), which is important in maintaining fecal continence.

The superior rectal artery is the direct continuation of the inferior mesenteric artery. The superior rectal artery anastomoses with branches of the middle rectal artery (a branch of the internal iliac artery) and with the inferior rectal artery (a branch of the internal pudendal artery).

Immediately superior to the perineal membrane is the deep transverse perineal muscle.

The anterior part of the tendinous arch of pelvic fascia forms the puboprostatic ligament in males or the pubovesical ligament in females. The posterior part of the tendinous arch of pelvic fascia forms the sacrogenital ligaments from the sacrum around the side of the rectum to attach to the prostate in the male or the vagina in the female.

Each obturator internus passes posteriorly from the lesser pelvis through the lesser sciatic foramen and turns sharply laterally to attach to the greater trochanter of the femur.

The tiny deferential artery usually arises from the inferior vesical artery and terminates by anastomosing with the testicular artery, posterior to the testis.

The internal iliac artery begins at the level of the fourth disc between L5 and S1 vertebrae, where it is crossed by the ureter. It is separated from the sacroiliac joint by the internal iliac vein and the lumbosacral trunk.