22 COMPARATIVE DENTAL ANATOMY 



performance of aerial flight. The limbs in the 

 Vertebrates are suspended from the vertebral 

 column, and constitute the appendicular skeleton. 

 There are never more than four limbs, sometimes 

 they are reduced to two, and in the snakes are 

 absent entirely. When present they are modified 

 to perform a variety of functions : such as swim- 

 ming in the water, flying in the air, running upon 

 the ground, climbing trees, seizing objects, etc. 



Eeproduction is performed by laying gelatinous 

 eggs by the fishes and batrachian reptiles by 

 eggs with a more or less hard shell in the higher 

 reptiles and birds, — hence oviparous, — and by the 

 young being born alive in some reptiles and 

 nearly all mammals, — hence viviparous. 



Comparative Anatomy is the study and com- 

 parison of the anatomy of lower animals with 

 the anatomy of Man. 



The comparative method of study is the only 

 scientific method, for one branch cannot be studied 

 alone, but must be illuminated by comparison with 

 kindred branches. Man is but an insignificant 

 part of nature, and is connected in the closest way 

 with the animal kingdom. His body is identical 

 with those of animals in its functions, and with 

 all Vertebrates, especially mammals, in its struc- 

 ture. Therefore his anatomy can only become 

 truly scientific through comparative anatomy and 

 his physiology through comparative physiology. 



