94 



COMPARATIVE DENTAL ANATOMY 



incisor-like form (Fig. 31) ankylosed to the jaw. 

 The Eel has small, conical, enamel-tipped teeth; 

 the Herring has minute, sharp-pointed teeth on 

 jaws and tongue; the Salmon has sharp-pointed 

 teeth distributed over the bones and cartilages of 

 the head, etc. Many varieties of teeth are found 



Fig. 31. — Sargus, incisor-form teeth ankylosed to jaw. Heterodont. 

 (Author's collection — Roentgenogram by Dr. E.' H. Skinner.) 



in this class, but all are related in arrangement 

 and structure. 



The Lung-fishes (Dipnoi) constitute a higher 

 type which possess both lungs and gills which per- 

 sist through life, in which they are closely related 

 to the lowest form of reptiles, the Batrachians, and 

 form the connecting link between fishes and rep- 

 tiles. In the Lepidosiren there are two sharp- 

 pointed recurved teeth, in the center of the jaw, 

 and posterior teeth with molar-like cusps. Den- 



