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 vertebre. 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 (IF oramen ischiadi- 
cum minus). The anterior border is concave, and completes the greater sciatic 
foramen (Foramen ischiadicum majus). 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 obturator internus and 
a vein pass through 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 by 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 pubie portion and extending backward, 
but commonly the ischia are in part not fused. The union is strengthened by 
white fibrous tissue dorsally and ventrally. A transverse band also covers the 
anterior border of the pubis, and other fibers (Lig. areuatum 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 fibrous tissue which covers the 
obturator foramen, leaving, however, a passage (Canalis obturatorius) for the 
obturator vessels and nerve. 
THE HIP JOINT 
This joint (Articulatio cox) 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 acetabulum 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-cartilage, the cotyloid ligament 
(Labrum 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 margin of the acetab- 
ulum and the neck of the femur. It is thickest laterally. 
The attachment on the femur is about 1 em. from the margin of the articular surface, except 
above, where 2 to 3 cm. of the neck is intracapsular. A thin, oblique band corresponding in direc- 
tion with the capsularis muscle reinforces the antero-lateral part of the capsule; this appears to 
be the feeble homologue of the very strong ilio-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 ligaments and the articular vessels. 
The round ligament (Lig. teres) is a short, strong band which is attached 
in the subpubie groove close to the acetabular notch, passes outward, and ends 
in the notch on the head of the femur (Fig. 581). 
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