452 ZOOLOGY 



Hind limbs developed. 



Nails of the digits hoof -like. 



Third and fourth digits equally devel- 

 oped, others reduced Artiodactyla. 



Third digit well developed, all ' 



others more or less reduced Perissodactyla. 



Five well developed digits Proboscidia. 



Nails claw-like. 



The front limbs modified to form wings, 



Cheiroptera. 

 No wings. 



Thumbs not opposable. 



Incisors and canines small, 



Insectivora. 

 Incisors chisel-shape and canines 



wanting Rodentia. 



Canines large; other teeth often pointed, 



Carnivora. 

 Thumbs opposable Primates. 



Order Edentata {toothless). — Placentalia in which the teeth 

 are absent or imperfect, being destitute of enamel and true roots. 

 They are found both in the Old World and in the New, especially 

 in the tropics of the southern hemisphere. The chief repre- 

 sentatives are the sloths and the hairy ant-eater of Central and 

 South America, the armadillo of South America and as far north 

 as Texas, and the scaly ant-eaters of Asia and Africa. The 

 sloths are sluggish vegetarians living in the trees, on the branches 

 of which they hang or climb, back downward, by means of their 

 long curved claws. The ant-eaters are almost wholly devoid of 

 teeth, but have narrow extensible tongues which they project 

 into ant-holes, capturing the ants by the sticky saliva. The 

 group furnishes a noteworthy exception to the statement that 

 the mammals lack an external skeleton. Overlapping bony 

 scales, or plates in the form of rings, may furnish a complete 

 armor by means of which they are kept from extermination in 

 spite of their inoffensive, sluggish habits. This is best seen in 

 the armadillo. 



