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 elements, 
however, actually take part in the formation 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 few 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 (facies 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 
