44 COMPARATIVE DENTAL ANATOMY 



The Attachment of Teeth in vertebrates pre- 

 sents four varieties or methods which grade into 

 one another in different degrees. They are as 

 follows : 



1st. By means of a Fibrous membrane (as in 

 the Sharks and Eays — Fig. 8), in which the teeth 

 are imbedded, and which carries them up over the 

 edge of the jaws. The teeth are brought up from 



Fig. 7. — Snout of Sawfish (Pristis pectinatus), showing teeth for 

 ripping open its prey. 



the floor of the mouth and rise up to replace those 

 which are lost from accident or use. These teeth 

 arise from the thecal fold. 



2nd. By Elastic Hinge (as in many fishes, the 



