OS ILIUM. 165 



cesses. In front the crest terminates in the anterior superior 

 spinous process ; below this is another protuberance, called 

 the inferior anterior spinous process ; and the edge of the bone 

 between these two processes is curved. 



Behind the crest terminates in the posterior superior spinous 

 process ; below this another protuberance is also observable, 

 (post. inf. spin, process) which is applied closely to the os 

 sacrum. Under this is a large notch, which, with the ligaments 

 that pass from the os sacrum to the os ischium, forms a foramen, 

 through which the great sciatic nerve, the pyriform muscle, 

 and some blood-vessels pass. 



The external surface, or, dorsum, of the os ilium, is greatly 

 undulated by the action of muscles that lie upon it ; the gluteus 

 maximus, on the posterior, and the gluteus medius and minimus, 

 on the anterior parts of it. The lower part of this bone, which 

 contributes to the formation of the acetabulum, is the thickest. 



The internal surface of the os ilium is concave, and supports 

 some of the intestines. From this concave surface a slight con- 

 cavity is continued obliquely forwards, at the inside of the 

 anterior inferior spinous process, where part of the psoas and 

 iliacus muscles, with the crural vessels and nerves pass. The 

 large concavity is bounded below by a sharp ridge, which runs 

 from behind forwards ; and, being continued with such another 

 ridge of the os pubis, forms a line of partition between the 

 cavities of the abdomen and pelvis. Into this ridge called linea 

 ilia innominata the broad tendon of the psoas parvus is 

 inserted. 



All the internal surface of the os ilium, behind the continu- 

 ance of this ridge, is very unequal : for the upper part is flat, 

 but spongy, where the sacro-lumbalis and longissimus dorsi 

 rise. Lower down, there is a transverse ridge from which 

 ligaments go out to the os sacrum. Immediately below this 

 ridge, the rough unequal cavities and prominences are placed, 

 which are exactly adapted to those described on the side of the 

 os sacrum. In the same manner, the upper part of this rough 

 surface is porous, for the firmer adhesion of the ligamentous 

 cellular substance ; while the lower part is more solid, and 

 covered with a thin cartilaginous skin, for its immovable arti- 



