THE PELVIC GIRDLE. 425 



ii. The middle digit has three phalanges, the proxi- 

 mal one being larg3 and lamellar, and the 

 distal one very small. 



iii. The postaxial digit has only a single phalanx. 



C. The Pelvic Girdle. 



The pelvic girdle consists of the same three elements on 

 each side ilium, ischium, and pubes as the mammalian 

 pelvis, from which, however, it differs widely in form. The 

 three component bones are firmly united to form the os 

 innominatum ; and at the junction of the three is the aceta- 

 bulum, or socket for the head of the femur, which is partially 

 membranous at its bottom. 



i. The ilium is an elongated lamellar bone, which 

 extends a considerable distance both in front 

 of and behind the acetabulum. Its inner 

 border is connected along nearly its whole 

 length with the sacral vertebrae and their 

 processes. The outer surface of the anterior 

 part is concave, that of the posterior part 

 convex : the inner surface of the bone forms, 

 with the adjacent vertebrae, two deeply concave 

 depressions in which the kidneys he. On the 

 outer surface, immediately behind and above 

 the acetabulum, is a projection, the anti- 

 trochanter, which bears on its outer surface 

 an articular facet for the great trochanter of 

 the femur, 

 ii. The ischium is a flattened lamellar bone pro- 

 jecting almost horizontally backwards from 

 the acetabulum, of which it forms about a 

 third. It is separated from the ilium, just 

 behind the acetabulum, by the oval ilio-sciatic 

 foramen, behind which the two bones are fused 

 together, 

 iii. The pubes is a long slender bar of bone which 

 projects downwards and backwards, parallel to 



