STRUCTURE OF THE VERTEBRATES 



87 



which are later lost. This order is heterogeneous and should be 

 divided into three orders. Simplicity of classification is the only 

 excuse for grouping them. Included here are the South American 

 ant eaters, sloths, armadillos; the genus IVIanis of Africa and the 

 Orient; and the Aard varks, or Gape ant eaters, of Africa. 



The armadillos are unique among living mammals in possess- 

 ing a heavy bony covering. This is arranged as scutes, or plates, 

 placed transversely to the axis of the body. The species are clas- 

 sified by the number of plates. When frightened the animal rolls 

 up, presenting a heavy defensive armor to any predaceous 

 animal. 



(Chiroptera) 

 Flying Adaptation 



Rlanis (Edentata) 

 a scale covered mammal 



Armadillo (Edentata) 



Fig. 35. Specializations of Mammalia. 



Manis is of particular interest to the anatomist on account of 

 the covering of ectodermal scales. These scales are reptile-like 

 in character and cover the entire body from head to tail. Be- 

 tween the scales are the hairs, usually in groups of three, one 

 group under each scale. Due to the evidence regarding the evo- 

 lution of the hair, it is thought that this represents the condition 

 found in the earlier mammals. 



Order Artiodactyla. The even-toed, herbivorous animals in- 

 clude the camels, sheep, cattle, deer, antelopes, pigs and hippo- 

 potami. These animals can be identified by the fact that the 

 weight is carried on the third and fourth digits, with the axis 



