78 



LAND MAMMALS IN THE WESTERN HEMISPHERE 



ample of the "ball and socket joint." In the inferior median 

 line the two pubes meet and may become coalesced, in a sym- 

 physis, the length of which differs in various mammals. The 

 pelvis and sacrum together form a short, wide tube, the diame- 

 ter of which is normally greater in the female skeleton than in 

 the male. 



The limbs are each divided into three segments, which 

 in the anterior extremity are the arm, fore-arm and hand 

 (or fore foot) and in the posterior extremity are the thigh, leg 

 and foot (or hind foot), and there is a general correspondence 

 between the structure of these segments in the fore and hind 

 legs, however great the superficial difference. The bones of 



the limbs, as distinguished from 

 those of the feet, are the long bones 

 and, except in a few very large and 

 heavy mammals, are essentially 

 hollow cylinders, thus affording 

 the maximum strength for a given 

 weight of bone; the cavity of a 

 long bone contains the marrow 

 and hence is called the medullary 

 cavity. In the young mammal 

 each of the long bones consists of 

 three parts, the shaft, which makes 

 up much the greater part of the 

 length, and at each end a bony 

 cap, the epiphysis. Growth takes 

 place by the intercalation of new 

 material between the shaft and the 

 epiphyses; when the three parts 



internal tuberosity. exU., external unite, grOWth CeaSCS and the ani- 

 tuberosity. 6c., bicipital groove. , . i i, 



dt, deltoid ridge, ah., shaft, s., ^^^'- IS adult. 



•supinator ridge, int. epi. internal The Superior Segment of the 



epicondyle. s.f. anconeal foramen. . . 



<r., trochlea. <r'. , trochlea, posterior fore limb has a single bouc, the 

 a'^nrone^Jw'"''' ^'''°°'''^' ^«™«™«' ^hg Upper end of which 



Fig. 25. — Left humerus of Wolf, from 

 the front and outer sides, the latter 

 somewhat oblique. A., head. int.t., 



