The Skull 105 



ads of creatures were changing in form and structure, 

 some growing too bulky and helpless and vanishing, 

 others developing powers of running, burrowing, flying 

 and leaping. But it is a very remarkable and wonder- 

 ful thing and very fortunate for us poor mortals, striving 

 after knowledge of the past, that in each general class 

 of creatures, certain ones should have found a niche 

 where they were removed from the fierce struggle for 



FIG. 81. Skull of young Alligator. Bones massive and solid, adapting their 

 owner to an active aquatic life but to sluggish terrestrial movements; eye- 

 cavities and brain-case very small, the jaws (organs of prehension) composing 

 by far the major part of the head. 



existence, and where for year after year, century upon 

 century, they and their descendants changed but little. 

 We might mention Amphioxus and sharks among fishes, 

 Necturus among amphibians, Sphenodon among reptiles, 

 and the duck-billed mammal and others among hair- 

 covered creatures. These may be meaningless names, but 

 if one will read about them and then examine their skins 

 and skeletons in our museums, many a glance will be 

 given into the ages of the past, compared to which the 



