662 MAMMALIAN ANATOMY 



which can be plainly felt in the living animal. It runs obliquely to 

 the long axis of the bone, but, owing to the oblique position of the 

 innominate in the body, its anterior and posterior ends are on about 

 the same level. The border is thin in front at the anterior superior 

 spine, but widens toward its termination behind 011 the posterior 

 superior spine. It is more or less rounded, and affords attachment 

 to tha sartorius muscle. 



The posterior border of the ilium is broad and flattened above, but 

 gradually becomes narrower and sharper, until at its lower end it is 

 thin and prominent. In its upper two-fifths it is rough for the attach- 

 ment of the gluteus medius muscle, and is prolonged inward on the 

 dorsal surface of the auricular process at the posterior inferior spine. 

 In its lower three-fifths it is smooth and concave from above down- 

 ward, producing the great sacro-sciatic notch and giving attachment to 

 the lower part of the gluteus minimus muscle. The posterior border 

 faces upward and backward. 



The Ischium forms the great part of the rest of the innominate. 

 It may be recognized as the stout L-shaped bone which lies above, 

 behind, and also partly below the obturator foramen ; it is that most 

 posterior part of the pelvis upon which the cat rests in sitting. It is 

 divided into a dorsal stout portion, the body, and a ventral flattened 

 bar, the ramus. The region about the swollen angle at the junction 

 of the two parts is known as the tuberosity of the ischium. 



The body is three times as long as wide, and prismatic on cross- 

 section. It presents three surfaces, the external (ventral), the internal 

 (dorsal), and the posterior (lateral), separated by three borders: the 

 external, extending from the dorsal border of the acetabulum to the 

 tuberosity ; the posterior, or dorsal, continuous with the posterior border 

 of the ilium ; and the internal, bounding the obturator foramen. 



The external surface (Fig. 518) is limited above and in front from 

 the ilium by the imaginary line through the upper part of the acetab- 

 ulum, dorsally by the posterior surface of the dorsal lip of the acetab- 

 ulum and by the external border, and ventrally from the pubes by an 

 imaginary oblique line in the acetabulum, and further back from the 

 obturator foramen by the internal border. Behind the foramen, the 

 surface is continuous behind and below with the outer surface of the 

 ramus. The outer lip of the tuberosity, which is the posterior limit 

 of the innominate, forms the posterior boundary of the external sur- 



