High-Yield Points:
• Pelvic cavity = bony funnel from pelvic inlet (sacral promontory + ilium + pubis) to pelvic outlet.
• Roof: sacrum + first few coccygeal vertebrae.
• Floor: pubis + ischium (pelvic symphysis).
• Side walls: pelvic surfaces of the ilium and ischium together with the sacrosciatic ligament and associated soft tissues.
• Pelvic inlet (anterior aperture): sacral promontory above, pectineal line of pubis below — measured for pelvimetry / dystocia prediction.
• Peritoneum forms pouches: pararectal, rectovaginal/rectogenital, vesicogenital, pubovesical fossae.
• Most of the pelvic viscera (rectum, bladder, urethra, accessory glands) become retroperitoneal caudally.

The Pelvic Cavity

The pelvic cavity is the space within the bony pelvis. Its inlet (cranial pelvic aperture) is circumscribed by the pelvic brim: the sacral promontory dorsally, the arcuate/iliopectineal lines laterally and the cranial border of the pubis ventrally. Its conjugate, transverse and oblique diameters are relevant to pelvimetry.

The outlet (posterior aperture) is bounded by the first coccygeal vertebra (dorsally), the sacrosciatic ligaments (laterally), and the ischial arch (ventrally).

Peritoneal Reflections: The peritoneum entering the pelvic cavity from the abdomen forms several pouches:
• Pararectal fossae — beside the rectum.
• Rectogenital pouch (rectovaginal in female; rectovesical in male) — between rectum and uterus/bladder.
• Vesicogenital pouch (in female) — between bladder and uterus.
• Pubovesical pouch — between pubis and bladder.
Caudally, the peritoneum stops short and the rest of the pelvic organs become retroperitoneal.