CHAPTER VII 



THE RISE OF THE MAMMALIA 



THE Mammals, comprising the most highly 

 organized animals with man at their head, are 

 characterized by a combination of features which 

 sharply distinguish them from their nearest living 

 relatives, the Reptiles. Among the more important 

 of these features are, the possession of a covering 

 of hair in place of the reptilian scales ; associated 

 with this character is the warm blood, kept at a 

 constant temperature ; the teeth arise in at most 

 two successions, whereas in Reptiles they may be 

 replaced an indefinite number of times, and whereas 

 in the Reptiles the teeth are all simple cones, in the 

 Mammal they are differentiated into several different 

 kinds, incisors in front for cutting, canines for de- 

 fence, premolars and molars for grinding. In the 

 skeleton a large number of peculiarities might be 

 enumerated. The vertebrae are divided into a con- 

 stant number of cervical, dorsal, lumbar and sacral 

 vertebrae ; the skull articulates with the vertebral 

 column by two occipital condyles, instead of one ; 

 the brain cavity is greatly enlarged, a sign of superior 



