THE ORIGIN OF MAN 81 



dentition or temporary teeth which eventually 

 fall out, and the permanent teeth which succeed 

 them. The heart is four-chambered as in the 

 other class of warm-blooded animals, the birds, 

 and the course of the blood through it is the same 

 in both. For a better description of the heart and 

 the motion of blood in animals Harvey's "On the 

 Motion of the Heart and the Blood in Animals' ' 

 is an excellent treatise. Most mammals have a 

 completely terrestrial habit while the seals, sea- 

 lions, sea-cows, whales and porpoises live in the 

 ocean. One order of wide distribution, the bats, 

 have developed the front limbs into wings, while 

 other stocks have lateral or body membranes be- 

 tween the limbs, and spreading these, glide from 

 tree to tree. 



The Tertiary opens with an archaic indigenous 

 mammal fauna, a most curious, strange and bi- 

 zarre assemblage, which is an advanced and di- 

 versified fauna, the descendants of Mezozoic 

 mammals. Later appear the modern animals and 



