Pelvic cavity

Pelvic cavity is the space enclosed by the pelvic bones. Anatomically, it corresponds to the true pelvis (lesser pelvis), which lies below the pelvic brim (pelvic inlet) and extends inferiorly to the pelvic outlet. Posteriorly, it is bounded by the the sacrum and coccyx, while anteriorly the right and left pelvic bones are joined at the pubic symphysis. Posteriorly, each hip bone articulates with the sacrum at the sacroiliac joint.

The region above the pelvic brim, enclosed between the iliac fossae of the hip bones, is known as the false pelvis (greater pelvis). Unlike the true pelvis, the false pelvis is considered part of the abdominal cavity.

The pelvic floor (pelvic diaphragm) divides the true pelvis into two anatomical regions: the pelvic cavity proper, which lies superior to the pelvic diaphragm, and the perineum, which lies inferior to it. The pelvic cavity proper contains the pelvic viscera, including the urinary bladder, rectum, and internal reproductive organs (e.g., the uterus and upper vagina in females, and the prostate and seminal vesicles in males).

Perineum

The perineum is a diamond-shaped region located inferior to the pelvic diaphragm. It is divided into two triangular regions by an imaginary line connecting the ischial tuberosities.

1. Urogenital triangle (anterior):

Bounded by pubic symphysis, ischiopubic rami, and ischial tuberosities. It contains openings for urogenital organs.

2. Anal triangle (posterior):

Bounded by the ischial tuberosities, sacrotuberous ligaments, and coccyx. It contains the anal canal, external anal sphincter, and the ischioanal fossae.

A strong fibrous sheet, the perineal membrane, further subdivides the perineum into superficial and deep perineal pouches. The perineal membrane is a triangular fascial layer that spans the gap between the ischiopubic rami and lies immediately inferior to the pelvic diaphragm.

Superficial perineal pouch

The superficial perineal pouch lies inferior to the perineal membrane, between membrane and the skin. It contains erectile tissues (corpora cavernosa and corpus spongiosum), together with ischiocavernosus, bulbospongiosus and superficial transverse perineal muscles.

Deep perineal pouch

The deep perineal pouch lies superior to the perineal membrane and inferior to pelvic diaphragm. It contains the membranous part of the urethra, the external urethral sphincter, the deep transverse perineal muscles, and in males, bulbourethral glands.