MAMMALS. 



105 



as a lion, while Diprotodon had a skull three feet in length 

 and a thigh-bone two feet from tip to tip. 



SUBCLASS III. PLACENTALIA. 



The great majority of mammals belong in this division. 

 They are marked off from the other subclasses by the 

 absence of those characters which have been mentioned as 

 distinguishing these, as well as by a structure now to be 

 mentioned. These mammals are not born until their in- 

 ternal organization has been well advanced; and in order 

 that they may be supplied with nourishment a peculiar 

 vascular structure is formed, the placenta, by means of 

 which blood is brought to the growing embryo. Such a 

 structure is lacking in both monotremes and marsupials. 

 The Placentalia are divided by details of structure into 

 many groups or orders, eleven of which are represented in 

 the world to-day. 



ORDER I. EDENTATA. 



The edentates, the lowest of the placenta! mammals, 

 receive their name from the fact that incisor teeth are 



FIG. 41. Nine-banded Armadillo (Dasypus novemcinctus). From Lutken. 



always lacking, while in the ant-eaters no teeth occur. 

 The feet are armed with strong claws. The group is a 

 tropical one, and has its greatest representation in Amer- 

 ica. Here belong the armadillos, in which the deeper 



