PELVIC GIRDLE OF VERTEBRATA. 



485 



buluni into two divergent pieces (Fig. 269), which enclose a large 

 opening (foramen obturatum). The anterior process is called the 

 pubis (P), the posterior one the ischium (Js). The two bones of either 

 side are more or less connected together along the middle line, 

 but this connection may disappear. The pelvis of the Crocodilini 



Fig. 269. View of the left side of the 



pelvis of Monitor. Jl Ilium. Js Ischium. 



P Pubis, a Hinder cud of the ilium, b Its 



anterior process. 



Fig. 270. View of the left side of the 

 pelvis of Alligator lucius. x y Two 

 limbs of the ischium, which unite with r s, 

 two processes of the ilium, to enclose a 

 foramen (o) at the base of the acetabulum. 

 The other letters as iu Fig. 269. 



(Fig. 270) differs from this in many points, for a single bone (Js) is 

 given off ventrally from the acetabulum, and is connected by means of 

 two processes with the ilium (x y). It appears to represent an 

 ischium only, while a bone, which takes no part in the acetabulum, 

 but articulates with the ischium (p), and converges, like its fellow, 

 towards the anterior wall of the abdomen, represents the pubis. 



The pelvis in the fossil Dinosaurii was of the same character ; 

 the ilium was distinguished by a process which was directed forwards, 

 and of which there is an indication only in the extant Saurii and 

 Crocodilini (b). The acetabulum was similarly incomplete, and was 

 connected with a long ischium, which was directed obliquely back- 

 wards and downwards, and was not united with its fellow of the 

 opposite side. A long pubis, which also ended freely, was given off 

 from the anterior margin of the acetabulum, and ran parallel to the 

 ischium. 



This relation of parts is the same as that which characterises the 

 Avian pelvis (Fig. 271). In them the ilium (J7) does not only 

 extend a long way back (a a), but its anterior process is converted 

 into a broad plate (b b). This extends along the lumbar region of 

 vertebral column, and even into the thoracic region, and so presses 

 a very large number of vertebras into the pelvic region. The ischium 

 (J*) runs backwards from the incomplete acetabulum, and in a 

 direction which is nearly parallel to that of the hinder portion of the 

 ilium ; the small pubis, which has a slight share in the formation 



