MAMMALIA. 44! 



Incisors chisel-shape and canines 



wanting Rodentia. 



Canines large; other teeth often 



pointed Carnivora. 



Thumbs opposable Primates. 



Order i. Edentata. 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, espe- 

 cially in the tropics of the southern hemisphere. The chief 

 representatives are the sloths, the hairy ant-eater and the arma- 

 dillo of South America, 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 down- 

 ward, 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 is primitive and degenerate, 

 and 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. 



Order 2. Sirenia. A small group of aquatic Placentalia, 

 more or less whale-like in form. They are sluggish, ungainly, 

 vegetable feeders. They have no posterior appendages and 

 the anterior are flipper-like, though capable of bending at the 

 elbow. They live near the shore and are represented by two 

 living genera, the sea-cow of our own eastern shores (Mana- 

 tee), and the Dugong of the Indian Ocean. 



Order j. Cetacea (Whales, Porpoises, etc.). The Cetacea 

 are aquatic mammals with a fish-like body. There are no 

 posterior appendages, and the anterior act as paddles, being 

 without joint. The tail is horizontally expanded into a pow- 

 erful paddle, and a dorsal fin is usually present. Teeth are 

 present in the embryo, but may be lost or replaced by " whale- 

 bone " in the adult. The stomach is chambered. The two 



