216 A MANUAL OF DENTAL ANATOMY. 



The teeth, which are situated upon the edge or exposed 

 "border of the jaw, are usually erect, whilst the rows which 

 lie behind them, farther within the mouth, point backwards, 

 and are more or less recumbent, not having yet come into 

 full use. 



In this respect, however, marked difference exists among 

 various genera of sharks ; for instance in the great tropical 



FIG. 92 ( l ). 



IN..S. 



white shark the teeth which lie on the border of the jaw 

 are erect, and all the successive rows are quite recumbent, 

 whereas in many of the dog-fishes the inner surface of the 

 jaws forms an even rounded surface along which the rows of 

 teeth are disposed in every intermediate position between 

 those fully recumbent at the innermost part of the jaw, 

 and those fully erected upon its exposed borders. Only a 

 few of the most forward rows of teeth are exposed, a fold 

 or flap of mucous membrane covering in those teeth which 



( 1 ) Lower jaw of Lamna. a. Edge of flap of mucous membrane which 

 covers in the teeth not yet completed. 



