PELVIC GIRDLE 391 



and at the junction of the three is the acetabulum, or socket 

 for the head of the femur, which is perforated at its bottom. 



i. The ilium is an elongated lamellar bone, which 

 extends a considerable distance both ia front 

 of and behind the acetabulum. Its inner 

 border is connected along nearly its whole 

 length with the sacral vertebrse 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 vertebrsB, two deeply concave 

 depressions in which lie the kidneys. On the 

 out^r 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 

 the lower border of the ischium. It forms a 

 very small part of the ventral border of the 

 acetabulum, in front of which it extends for- 

 wards as a blunt pre-pubic process, corre- 

 sponding to the pubes of mammals. 



Behind the acetabulum, the pubes and 

 ischium are separated by the sht-Uke obturator 

 foramen, behind which the two bones are 

 fused for a short distance. The hinder end of 

 the pubes is thickened, and extends some 

 distance beyond the ischium. 



