SYMPHYSIS PELVIS — OBTURATOR MEMBRANE 



191 



quadrilateral sheet which completes the lateral pelvic wall. Its upper border is 

 attached to the border of the sacrum and the transverse processes of the first and 

 second coccygeal vertebrae. Its lower border is attached to the superior isehiatic 

 spine and tuber ischii. Between these it bridges over the external border of the 

 ischium and completes the lesser sciatic foramen. The anterior l)order is concave, 

 and completes the greater sciatic foramen. The posterior border is fused with the 

 vertebral head of the seniimeml)ranosus muscle. 



The ilio-lumbar ligament (Ligamentum ilio-lumbale) is a triangular sheet which 

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

 ilium below the attachment of the longissimus nmscle (Fig. 184). 



Ventral sacro-iliac ligament 



^ Exlvrnal angle 

 ) (if ilium 



Sacro-iliac articulation 



Depression for origin of inner tendon of 

 biceps femoris 



Posterior part of trochanter major 

 Anterior part of trochanter 

 major 



Trochanter minor 



Fig. 153. — Left Os Cox.e and Adjacent Parts of Sacrum and Femur of Horse. (After Schmaltz, Atlas 



d. Auat. d. Pferdes.) 



SYMPHYSIS PELVIS 

 The symphysis pelvis is formed by the junction of the two ossa cdxarum at 

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

 cartilage; in the adult the latter is gradually replaced by bone, the process beginning 

 in the pubic portion and extending backward. The union is strengthened by white 

 fibrous tissue above and below, and a transverse band also covers the anterior border 

 of the pubis (pecten). No appreciable movement occurs even before synostosis 

 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. 



