98 SKELETON. 



processes is another concavity, from which the anterior edge of 

 the gluteus medius arises. 



The posterior margin of the ilium is also very unequal, both 

 in its direction and thickness. The posterior inferior spinous 

 process is about sixteen lines below the posterior superior, and 

 terminates a cutting edge running between these two processes. 

 Just below it we find the d*eep excavation called the sciatic 

 notch, through which pass out the pyriform muscle, the sciatic 

 nerve, and several blood vessels. 



The exterior face of the ilium, called its dorsum, is generally 

 convex and rounded; its margins, however, are so elevated, that 

 partial depressions, or sinkings below the general surface, may 

 be remarked, especially at its back part. Just above the two 

 posterior spinous processes, a flatness is observable, from which 

 a part of the gluteus magnus arises. A semicircular rough 

 ridge begins at or near the anterior superior spinous process, 

 and may be traced on this surface of the bone to the sciatic 

 notch. All that portion of the dorsum between this ridge and 

 the spine, with the exception of the little flat surface just above 

 the posterior spinous processes, gives origin to the gluteus me- 

 dius. The dorsum terminates below at the acetabulum, and be- 

 tween the latter and the semicircular ridge is the surface for the 

 origin of the gluteus minimus. 



The internal face of the ilium, or that which looks towards 

 the belly, is called its costa or venter. Its superior part, amount- 

 ing to about two-thirds of the whole surface, is very concave, 

 and is the iliac fossa, which is occupied by the iliacus internus 

 muscle. The fossa is continued forwards into the hollow below 

 the anterior inferior spinous process, and over the acetabulum. 

 The iliac fossa is terminated below by a rounded ridge, a part of 

 the linea ilio-pectinea that separates the greater from the lesser 

 pelvis. The remaining third of the costa of the ilium is very 

 rough and unequal, and is appropriated to the articulation with 

 the sacrum, and to the origin of some of the muscles of the back. 

 Immediately posterior to the sciatic notch is the surface for the 

 sacrum, which is somewhat triangular, but irregularly so, and 

 extends from the iliac fossa to the posterior inferior spinous 

 process. Behind the sacral surface is another, twice as large, 

 strongly marked by its roughness, and elevated into a vertical 

 ridge at its middle. Anterior to this ridge arise many of the 



