io FIELD MUSEUM OF NATURAL HISTORY ZOOLOGY, VOL. XL 



few hibernate during the cold weather. The majority of mammals are 

 thickly covered with hair, but a few are provided with an armor of 

 hard, scaly plates (Armadillos); and others, with long, sharp quills 

 (Porcupines). In size they vary from the tiny Shrew to the gigantic 

 Sulphur-bottom Whale, having a length of 85 feet or more and a weight 

 of as many tons. 



THE OSSEUS SYSTEM. 



Having learned what mammals are, it is essential that the student 

 should know something of their anatomy. To enable him to study 

 them intelligently he must know at least the names and locations of 

 the more important bones of the skeleton. For ordinary purposes this 

 can be learned better from a chart than from detailed descriptions, 



8 



Skeleton of a Bear. 



a,- Skull; b, vertebral column or back-bone; c, cervical vertebrae; d, dorsal vertebrae; e, lumbar 

 vertebra; f, sacral vertebras; g, caudal vertebrae; h, ribs; i, humerus; j, ulna; 1, radius; m, meta- 

 carpals; n, carpal bones or carpus; o, phalanges; p, femur; r, tibia; s, fibula; t, metatarsals; 

 u, phalanges; v, tarsal bones; w, scapula; x. pelvic girdle or hip bone 



food scarcity. The condition varies in duration and intensity in different mammals. 

 Some hibernate for only short periods during the coldest weather, while others 

 remain for months in a comatose condition. In the latter the bodily temperature 

 and action of the respiratory organs are greatly affected. While undoubtedly 

 due originally to climatic conditions, the habit has become hereditary, as illustrated 

 by certain southern species, which continue to hibernate when the occasion for it 

 no longer exists. Further remarks are unnecessary here, as the subject is discussed 

 more fully ater in connection with the habits of the various species. 



