94 ATLAS AND TEXT-BOOK OF HUMAN ANATOMY. 



Fig. 132. — The right innominate bone seen from the outer surface (£). 

 Fig. 133. — The right innominate bone seen from the inner surface (?). 



foramen. It is composed of a body (Fig. 134) and of two rami, a superior and an inferior 

 ramus, which, like those of the pubic bone, form boundaries of the obturator foramen. 



In the adult innominate bone the thickened and somewhat constricted portion of the bone, 

 upon whose outer surface is the acetabulum, gives off a bony plate, the ala of the ilium (Fig. 

 134), which passes upward and presents an external convex and an internal concave surface. 

 Below and in front of the acetabulum, the middle portion of the bone sends out a second plate, 

 which is perforated by the obturator foramen (rami of the pubis and ischium). 



The ala of the ilium (Fig. 137) is shaped like the horns of a buck, without the tips. In 

 the middle it is frequently as thin as paper. Its superior margin is markedly thickened and 

 rough and is known as the crest of the ilium, and upon this crest are three rough lines, produced 

 by the attachment of the abdominal muscles. They are most distinct in the middle of the iliac 

 crest, where it is thickest and reaches its greatest height, and are termed the external, the 

 internal, and the middle lips of the crest (Figs. 132 and 134). 



Anteriorly the crest of the ilium ends in a spine, the anterior superior spine (Figs. 132 to 

 134), and at the posterior extremity of the crest there is another less pronounced spine, the pos- 

 terior superior spine (Fig. 131). Below the posterior superior spine, and separated from it by 

 a shallow notch, is the posterior inferior spine, and below this the posterior margin of the 

 innominate bone presents a deep paraboloid notch, the great sciatic notch (Fig. 132), whose 

 upper boundary is formed by the posterior margin of the ala, and its antero-inferior one by 

 the bodies of the ilium and ischium. 



Below the anterior superior spine at the anterior border of the body of the ilium is situated 

 the anterior inferior spine (Figs. 132 to 134). It is placed at a greater distance from the anterior 

 superior spine than is the posterior inferior from the posterior superior one, and is situated im- 

 mediately above the upper and anterior margin of the acetabulum. 



The external surface of the ala of the ilium (Fig. 132) is rough and convex, and presents 

 three rough lines which indicate the areas of origin of the gluteal muscles. These lines are 

 designated as the posterior or superior, the anterior or middle, and the inferior gluteal lines. 

 The posterior gluteal line is almost vertical and runs across the posterior portion of the ala 

 of the ilium to the upper boundary of the great sciatic notch, and the small area of the ilium 

 which it bounds gives origin to a portion of the glutaeus maximus muscle and contains both 

 posterior spines. 



The long anterior line passes backward in an arched manner from the anterior superior 

 spine; it is at first almost horizontal, then nearly vertical, and ends near the superior line at 

 the upper margin of the great sciatic foramen. The surface of the ala included between it and 

 the superior line gives origin to the glutaeus medius muscle. 



The inferior line is considerably shorter than the anterior one. It commences between the 

 anterior superior and anterior inferior spines and passes backward almost horizontally above 

 the acetabulum to the middle of the great sciatic foramen. It is but slightly curved and is apt 



