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I. Orientation of Pelvis

II. Osteology

III. Joints

IV. Ligaments

V. Pelvic Musculature

VI. Perineum

[WebLecture Slide 22 320x240 pixels]

WebLecture Slide 22

The obturator internus muscle originates within the pelvis on the obturator membrane (a membrane that closes all but the superior border of the obturator foramen) and on those portions of the pubis and ischium that surround the obturator foramen. Though broad in origin, the muscle tapers to a narrow tendon that passes through the lesser sciatic foramen and rides over the ischial body (over a bursa) just superior to the ischial tuberosity to attach on the medial aspect of the greater trochanter of the femur. The course of the muscle as it originates from the obturator membrane is primarily posterolateral, but as the muscle courses over the ischium, it turns sharply laterally, making nearly a 90o turn. The body of obturator internus covers a broad expanse of the interior walls of the pelvis. When viewed from the posterior or gluteal aspect, the tendon of the obturator internus is often obfuscated by the tendons of the superior and inferior gemellus muscles (the two gemelli). The orientation and course of the obturator internus muscle is not intuitive. Exercises with the 3D models presented here, a bony pelvis or a dissected cadaver are strongly encouraged for study. The obturator internus (also a lateral rotator of the thigh) is innervated by sacral nerves 1 and 2 through small branches of the sacral plexus. We will learn later that a major part of the pelvic diaphragm attaches to the fascia of the obturator internus.
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