314 



BRANCH CHORDATA 



of them are attached anteriorly to the sternum, which is always 

 present, and posteriorly to the vertebrae, but there are also a 

 number of floating ribs or those attached posteriorly only. 



The pectoral girdle consists of two bones on each side, the 

 scapula (Fig. 257) and the clavicle. The clavicle is absent 

 in ungulates, which use their fore limbs mainly for support and 

 in walking, but it is well developed in " flying," digging, or 

 burrowing mammals. 



Fig. 257. Anterior limb of man, dog, hog, sheep, and horse: tic, Shoulder- 

 blade ; c, coracoid ; a, b, bones of forearm ; 5, bones of the wrist ; 6, bones of 

 the hand; 7, bones of the fingers. (Le Conte's "Geology," American 

 Book Co., Publishers.) 



The pelvic girdle (Fig. 256) consists, normally, of the os in- 

 nominatum on each side. There are "four distinct elements in 

 each one: the ischium, the ilium, the pubis, and the cotyloid." 1 



The limbs which raise the body from the ground and are the 

 principal organs of locomotion are four in number, except in 

 Sire'nia and Cetacea, where there are no externally visible hind 

 limbs. Rudiments of the pelvis are found in both of these orders, 

 and in some of the Cetacea rudiments of the femur and of the 

 tibia. The bones of both anterior and posterior limbs (Figs. 257, 



1 Beddard, " Mammalia," p. 41. 



