SYMPHYSIS PELVIS — THE HIP JOINT 231 



Its dorsal border is attached to the border of the sacrum and the transverse processes 

 of the first and second coccygeal vertebras. Its ventral border is attached to the 

 superior ischiatic spine and tuber ischii. Between these it bridges over the lateral 

 border of the ischium and completes the lesser sciatic foramen (Foramen ischiadi- 

 cum minus). The anterior border is concave, and completes the greater sciatic 

 foramen (Foramen ischiadicum iiTiajus). The posterior border is fused with the 

 vertebral head of the semimembranosus muscle. 



The lesser sciatic foramen is closed, except where the tendon of the oliturator internus and 

 a vein pass thi'ough it, by a thin fibrous sheet given off from the sacro-sciatic ligament. 



The ilio-lumbar ligament (Lig. ilio-lumbale) is a triangular sheet which at- 

 taches the ends of the lumbar transverse processes to the ventral surface of the 

 ilium below the attachment of the longissimus muscle (Fig. 273). 



SYMPHYSIS PELVIS 



The symphysis pelvis is formed l^y the junction of the two ossa coxarum at 

 the ventral median- line. In the young subject the bones are united by a layer of 

 cartilage (Lamina fibrocartilaginea) ; in the adult the latter is gradually replaced 

 by bone, the process beginning in the pubic portion and extending backward, 

 but commonly the ischia are in part not fused. The union is strengthened by 

 white fibrous tissue dorsally and ventralh\ A transverse band also covers the 

 anterior border of the pubis, and other fibers (Lig. arcuatum ischiadicum) extend 

 across at the ischial arch. No appreciable movement occurs even before synosto- 

 sis takes place. 



OBTURATOR MEMBRANE 

 This (Membrana obturatoria) is a thin layer of fil)rous tissue which covers the 

 obturator foramen, leaving, however, a passage (Canalis obturatorius) for the 

 obturator vessels and nerve. 



THE HIP JOINT 



This joint (Articulatio coxsb) is an enarthrosis formed by the proximal end of 

 the femur and the acetabulum. 



Articular Surfaces. — The head of the femur presents an almost hemispherical 

 articular surface, which is continued a short distance on the upper surface of the 

 neck. It is more extensive than the socket which receives it. It is cut into medi- 

 ally by a deep notch for the attachment of the round and accessory ligaments. 

 The acetabulmn is a typical cotyloid cavity. Its articular surface is somewhat 

 crescentic, being deeply cut into medially by the acetabular notch and fossa. 



The acetabulum is deepened by a ring of fibro-cartilagc, the cotyloid Ugament 

 (Labrtmi glenoidale), which is attached to the bony margin; that part of the liga- 

 ment which crosses the notch is called the transverse acetabular ligament (Lig. 

 transversum acetabuli) (Fig. 291). 



The joint capsule is roomy. It is attached around the margm of the acetab- 

 ulum and the neck of the femur. It is thickest laterally. 



The attachment on the femur is about 1 cm. from the margin of the articular surface, except 

 above where 2 to 3 cm. of the neck is intracapsular. A thin, obhque band correspondmg m du-e^c- 

 tion with the capsularis muscle reinforces the antero-lateral part of the capsule; this appears to 

 be the feeble homologue of the very strong iUo-femoral ligament of man The_ capsule is very 

 thin under the ilio-psoas, and is adherent to the, muscle. Its fibrous part is perforated medially 

 by the accessory and round Ugaments and the articular vessels. 



The round ligament (Lig. teres) is a short, strong band which is attached 

 in the subpubic groove close to the acetabular notch, passes outward, and ends 

 in the notch on the head of the femur (Fig. 581). 



