164 



HIGH SCHOOL ZOOLOGY. 



with their different function are reduced to three {Brady- 

 pus) (Fig. 110, F) or two (Choloe^ms). Very complete remains 

 of extinct forms intermediate between these two subdivisions 

 of the order have been found in South America ; these include 

 gigantic forms like Megatherium, almost as large as an elej>hant, 

 which probably fed on the foliage of trees, uprooted by their 

 powerful limbs. 



Fig. 110. Maiius of various Mammalia. 



P, Horse. D, Dolphin. E, Elephant. A, Orang. T, Tiger. O, Ox. F, Sloth. 



il, Jlole. r, radius, c, carpus, m, metacarpus, s, sesamoid bone. 



ph, phalanges, ds, dew-claws. 



21. A second aberrant order is that of the Cetacea, which 

 owe their peculiarities to their aquatic life. This is not the 

 only order of Mammalia in which aquatic habits are present, for 

 certain carnivorous animals like the seals, sea-lions and walruses, 

 are exclusively or almost exclusively confined to water, yet in 

 the Cetacea, this adaptation is carried so far as to isolate thtem 

 from the othei' orders of the sub-class to which they belong. 



