OF EVOLUTION. 



79 



and birds, and in probably equal degree. I have 

 placed before you a drawing of one of the lar- 

 gest of the dinosaurian reptiles, the Jurassic Bron- 

 tosaurus, an animal measuring probably fifty feet 

 in length, yet in which the weight of the entire 

 skull does not appear to have exceeded that of 

 the fourth vertebra of the neck. 



7, Skull of Mastodon Americanus, Pliocene and Post-Pliocene. 

 (After Marsh.) 



