1. MUSCLES of the PELVIS

2. Pelvic Walls: Obturator internus Origin: Origin: Most of the internal surface of the anterolateral wall of the pelvis minor (pelvic surfaces of the ilium, ischium, and obturator membrane). Insertion: Insertion: Greater trochanter of femur (medial surface) via strong tendon which passes through the lesser sciatic foramen.

3. Pelvic Walls: Obturator internus Action: Action: Lateral thigh rotation (when hip is flexed); helps to hold femoral head in acetabulum. Nerve: Nerve: Nerve to obturator internus (L5-S1).

4. Pelvic Walls: Piriformis Origin: Origin: Anterior aspect of the second through the fourth lateral masses of the sacrum and the sacrotuberous ligament. Insertion: Insertion: Greater trochanter of the femur–superior border.

5. Pelvic Walls: Piriformis Action: Action: Lateral rotation of thigh (when hip is extended); thigh abduction (when hip is flexed); helps to hold femoral head in acetabulum; forms the muscular bed for the sacral plexus; leaves the pelvis via the greater sciatic foramen. Nerve: Nerve: Ventral rami of S1-2.

6. Pelvic Diaphragm: Levator Ani Composed of three muscles: Composed of three muscles:Puborectalis.Pubococcygeus.Iliococcygeus. Figure 3.39 Figure 3.39

7. Pelvic Diaphragm: Levator Ani Puborectalis: Puborectalis: Origin:Pectin pubis. Insertion:Rectum and anal canal. Action:Maintain anorectal flexure. Compress abdominal viscera. Compress pelvic contents. Nerve:Perineal nerve.

8. Pelvic Diaphragm: Levator Ani Pubococcygeus: Pubococcygeus: Origin:Pectin pubis. Insertion:Coccyx. Action:Raise pelvic floor. Compress abdominal viscera Compress pelvic contents. Nerve:Perineal nerve.

9. Pelvic Diaphragm: Levator Ani Iliococcygeus: Iliococcygeus: Origin:Obturator fascia and ischial spine. Insertion:Coccyx and anococcygeal ligament. Action:Same as for pubococcygeus. Nerve:Perineal nerve.

10. Pelvic Diaphragm: Coccygeus Part of pelvic diaphragm. Part of pelvic diaphragm. Not part of levator ani. Not part of levator ani. Origin:Ischial spine. Origin:Ischial spine. Insertion:Inferior sacrum and coccyx. Insertion:Inferior sacrum and coccyx. Action:Support pelvic viscera. Flex coccyx. Action:Support pelvic viscera. Flex coccyx. Nerve:S4, S5 Nerve:S4, S5