Chapter 5: Pelvis & Perineum: Pelvic Organs & Floor Anatomy

Pelvis & Perineum: Pelvic Organs & Floor Anatomy begins by establishing the osteological framework, detailing the articulation of the two pelvic bones with the sacrum and coccyx to form the bony pelvis, while distinguishing between the false (greater) pelvis located in the abdominal cavity and the true (lesser) pelvis, which defines the pelvic inlet and outlet. The text thoroughly examines the structural boundaries of the pelvic cavity, describing the lateral walls formed by the obturator internus and piriformis muscles, and the critical pelvic floor or diaphragm, composed of the levator ani and coccygeus muscles, which supports the viscera and plays a vital role in maintaining continence. The description then transitions inferiorly to the perineum, a diamond-shaped area divided into the anterior urogenital triangle and the posterior anal triangle. This section delineates the complex layering of fascia and muscle, including the perineal membrane, the deep perineal pouch containing the external urethral sphincter, and the superficial perineal pouch which houses the erectile tissues and associated muscles of the external genitalia. A significant portion of the chapter is dedicated to the pelvic viscera, systematically reviewing the terminal gastrointestinal tract (rectum and anal canal), the urinary system (ureters, bladder, and urethra), and the reproductive organs. It contrasts the male and female anatomy, detailing the course of the urethra, the structure of the prostate, seminal vesicles, and testes in men, versus the uterus, ovaries, uterine tubes, and vagina in women. The text explains the crucial support mechanisms for the uterus, including the broad ligament and cardinal ligaments, and identifies clinically important peritoneal recesses such as the recto-uterine pouch (pouch of Douglas). Neurovascular supply is extensively covered, mapping the branches of the internal iliac artery and the intricate venous plexuses that drain the region. The somatic innervation via the sacral and coccygeal plexuses, specifically the sciatic and pudendal nerves, is described alongside the autonomic control of pelvic organs through the superior and inferior hypogastric plexuses, which regulate functions such as erection and micturition. The chapter concludes by integrating surface anatomy and clinical correlates, discussing pathologies like pelvic fractures, organ prolapse, ectopic pregnancy, and nerve compression.