THE METABOLIC IVIACHINERY OF AMMAJ.S 



285 



Teeth are found in the vertebrate group from fishes up to man. 

 While derived from a common embryological source, they have 

 developed in many different ways during the course of e\olution to 

 serve such various uses as grasping, grinding, or cutting food. In 



skull 



frontal 



Sinus 



turbirTok/.V 



inteTTjol 

 nostrij. 



external 

 nostril 



SCCtlp 



ctura mater 



pineal glanct 

 pitccito-ry 

 "pons 



cersbellum 

 --mectulicc 



cpiglotti: 

 larynx 



trcuibea.... 

 esophagus 

 thyroid. 



Sagittal section of human head. 



many of the lower fishes they are unspecialized and are continu- 

 ously being replaced as worn out. Thus the shark always has a 

 new set developing behind the old, a device suggestive of an end- 

 less chain. 



The garpike has a series of long, pointed, unspeciahzed teeth which 

 are used merely as holdfast organs. In such types, teeth are not 

 crushing or tearing devices. The amphibia and reptiles show little 

 tendency toward specialization, except among the poisonous reptiles 



X . V. Sinir CnnxcnaHo)! />ipl. 



Unspecialized teeth of the garpike, Lc/x'sosleus ossciis. 



