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Chapter 6
The pelvis
THE BONY PELVIS, MUSCLES AND LIGAMENTS (Figs 6.1-6.6)
CHAPTER CONTENTS
The bony pelvis, muscles and ligaments The pelvic floor 217 The sigmoid colon, rectum and anal canal
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Blood vessels, lymphatics and nerves of the pelvis The lower urinary tract 227 The male urethra 228 The male reproductive organs 229 The female reproductive tract 236 Cross-sectional anatomy 242
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The pelvis (Fig. 6.1) is a bony ring comprised of paired innominate bones, the sacrum and coccyx. The innominate bones articulate with each other anteriorly and with the sacrum posteriorly. Each innominate bone is composed of three parts, which fuse at the acetabulum. The ilium is a flat curved bone and bears the iliac crest superiorly. The anterior and posterior superior iliac spines are on either end of the iliac crest, with the anterior and posterior inferior iliac spines below them. The inner surface of the bone is smooth and has the iliopectineal line running from front to back, demarcating the true from the false pelvis. The pubic bone consists of a body, and inferior and superior rami. The body of the pubic bone articulates with its fellow at the symphysis pubis. It bears a tubercle on its superomedial aspect. The articular surfaces of the symphysis pubis are covered in hyaline cartilage with a fibrocartilaginous disc between them. The pubic bone is strengthened on all sides by dense ligaments. The ischium is composed of a body and an inferior ramus, which joins the inferior pubic ramus. The body bears a tuberosity inferiorly and a spine posteriorly. The ischial spine defines the greater and lesser sciatic notches above and below. The obturator foramen is bounded by the body and rami of the pubic bone and the body and ramus of the ischial bone. The sacrum Five fused vertebrae comprise this triangular bone, which is curved posteriorly. The anterior part of its upper end is termed the sacral promontory. It articulates with the lumbar spine superiorly and with the coccyx inferiorly. Anteriorly the sacrum has four pairs of sacral foramina, which transmit nerves from the sacral canal. Lateral to these are the lateral masses or alae of the sacrum. The sacrum also bears four pairs of posterior sacral foramina
