570 



Comparative Morphology of Chordates 



(J 



Fig. 111. Modifications of the forelimb. (a) Necturus, a salamander, (b) Ichthyo- 

 saurus, an extinct marine reptile, (c) Globicephalus, a cetacean (dolphin), (d) 

 Pterodactyl, an extinct flying reptile. (The digits were probably I- IV, not II-V as 

 shown by Wilder.) (e) Bird, (f) Bat. 



(a) represents a slightly modified limb skeleton — one digit lacking; (b) and (c), 

 limbs modified for swimming; (d), (e), and (f), those modified for flight. (H) 

 Humerus; (r) radius; (u, articulating with H) ulna; (I-V) digits. In (b) a typical 

 carpus may be recognized: three proximal bones (v,i,u), five distal bones (1-5), and 

 two centralia (ci, c 2 ). (Courtesy, Wilder: "History of the Human Body," New 

 York, Henry Holt & Co., Inc.) 



Certain omnivorous bipeds use the forepaws to hold a knife and fork 

 by which they manipulate their food. And some mammals swim, dive, 

 or fly. In speed of locomotion they range from the arboreal sloth which, 

 on the ground, merely crawls along, to the horse, greyhound, and 

 antelope, and the cheetah, a long-legged Asiatic and African catlike 

 carnivore, which can overtake an antelope. For each of these many 

 modes of use, the legs are anatomically adapted (Fig. 441). 



In general mode of life, some mammals — especially the smaller 

 and the herbivorous — are timid and retiring in disposition. Others are 

 powerful, predacious, and, in general, aggressive. Still others, such as 

 the elephant, hippopotamus, and other large herbivores, by virtue of 

 great bulk of body and a thick hide, have no need of being timid and 

 retiring, yet ordinarily are not aggressive. 



Types of Mammals 



Every animal must be anatomically fit for a particular environ- 

 ment, diet, mode of locomotion, and pattern of behavior. Mammals, 

 emerging from the reptile-dominated Mesozoic Age, advanced into a 

 friendlier Cenozoic which gradually opened up before them an almost 



