The Skeleton of the Posterior Limb. 167 



acetabulum, which is the basin-like depression for the articulation 

 of the pelvis with the femur. Only two of the original element s, 

 howe ver, actually take part in the form ation of the acetabulum, 

 the pubis being excluded through the development in the acetabular 

 depression of a small triangular element, the OS acetabuli. 

 Although completely coalesced in the adult condition, and showing 

 but tew traces of their original separation, the three chief elements 

 are nevertheless described as if distinct. 



The ilium (os ilium) is the anterior, also somewhat dorsal, 

 portion of the bone; that part extending forward from the ace- 

 tabulum. It comprises a basal portion, the body (corpus oss. 

 ilium), which includes the anterior portion of the acetabulum and 

 the cylindrical part of the bone in front of it, and an expanded 

 portion, the iliac wing (ala oss. ilium), for muscle attachment and 

 articulation with the sacrum. The body is somewhat triangular 

 in section, its surface being divided into three areas, which are 

 respectively medial, or sacral, ventrolateral, or iliac, and dorso- 

 lateral, or gluteal. The corresponding borders are respectively 

 ventral, or pubic, lateral, or acetabular, and dorsal, or ischial. 

 The acetabular border terminates a short distance in front of the!' 

 acetabulum in an abruptly truncated projection, the inferior 

 anterior spine (spina anterior inferior). The ischial border forms 

 the anterior half of a long depression of the dorsal surface of the 

 coxal bone, the greater sciatic notch (incisura ischiadica major). 

 The pubic border presents on its medial side a faint, ridge-like 

 elevation, the iliopectineal line (linea iliopectinea), which con- 

 nects the sharp anterior border of the pubis with the articular 

 surface for the sacrum. 



The wing of the ilium forms a shovel-like expansion, the 

 natural position of which is almost sagittal. Its lateral surface 

 provides a fairly extensive area for the origin of the gluteal muscles. 

 Its medial surface is a muscle surface only in its anterior portion, 

 the posterior portion being occupied by the roughened, auricular 

 surface (fades auricularis), for connection with the sacrum. 

 The dorsal margin is thin and. straight. Posteriorly, where it is 

 associated, with the greater sciatic notch, there is a small projection, 

 the inferior posterior spine (spina posterior inferior), also termed 

 the tuber sacrale. Anteriorly it passes by a broad angle into the 



