484 COMPARATIVE ANATOMY. 



(Hipparion), and when the two lateral fingers are reduced to their 

 metacarpals alone, these are attached to the large metacarpus of the 

 third finger as mere "splint-bones" (VI), and the third finger 

 becomes the sole support of the limb (Eqinis). 



The number of phalanges in the different fingers is increased in the 

 Cetacea only ; all other Mammals have two in the pollex, and three 

 in all the other fingers. 



Posterior Appendages. 



Pelvic Girdle. 

 § 366. 



The relations of the pelvic girdle are also correlated with 

 differences in the functions of the extremity. The homology 

 between the two skeletal portions is consequently more fully recog- 

 nisable as the functions of the two extremities are more nearly 

 the same, and the extent to which they are differentiated from 

 one another less. 



A single piece of cartilage forms the groundwork of the pelvic 

 girdle. In the Selachii this is rarely enlarged in a dorsal direction. 

 In the Ganoi'dei and Teleostei the two halves of the ossified portion 

 are connected in the middle line. They undergo considerable varia- 

 tions in position, for they may be placed more or less anteriorly and 

 close to the shoulder-girdle (Pisces thoracici), or may even be united 

 with it (Pisces jugulares). 



In the Amphibia the two bones of the pelvis are connected with 

 the vertebral column ; at the same time they may be seen to be 

 divided into two pieces at the point where they are connected with 

 the femur ; the dorsal one, which is attached to a transverse pro- 

 cess (that is, to a rudimentary rib), forms the ilium ; the ventral one, 

 which is connected along the middle line with its fellow of the 

 opposite side, is known as the ischio-pubic bone (Urodela). There is 

 reason, however, for supposing that it merely corresponds to an 

 ischium. This arrangement is modified in the Anura (cf. Fig. 225), 

 for the long and slender ilia (11) are uuited with the ischio-pubic 

 bones (is), which are converted into a vertical disc, and fused with 

 one another. 



The ilium of the Reptilia is greatly developed ; in Chamasleo it 

 resembles a scapula, and is continued into a process, which is com- 

 parable to a supra-scapula. In the Saurii it is elongated (Fig. 269, 

 Jl) ; in the Crocodilini it is shorter and broader (Fig. 270, J7). The 

 bone is directed forwards, so that it is connected with 

 the sacrum behind the acetabulum. In the Saurii and Ohe- 

 lonii the ventral portion of the pelvis is continued from the aceta- 



