THE SKELETON IN FISHES. THE TEETH. 



107 



bones of the mouth, and also on the hyoid and branchial 

 arches. The teeth are all originally developed in the mucous 

 membrane of the mouth, but they afterwards generally become 



5-' 



FIG. 14. DIAGRAM OF A SECTION THROUGH THE JAW OF A SHARK (Odontaspis 



americanus) showing the 

 specimen and diagram). 



1. teeth in use. 



2. teeth in reserve. 



3. skin. 



4. cartilage of the jaw. 



5. encrusting calcification 



succession of teeth (Brit. Mus. from 



cartilage. 



6. connective tissue. 



7. mucous membrane of the 



mouth, 

 of 



attached to firmer structures, especially to the jaws. In 

 Elasmobranchs, however, they are generally simply imbedded 

 in the tough fibrous integument of the mouth. Their attach- 

 ment to the jaws may take place in three different ways. 



(1) By an elastic hinge-joint, as in the Angler (Lophius), 

 and the Pike (Esox lucius). In the Angler the tooth is held 

 by a fibrous band attaching its posterior end to the subjacent 

 bone, in the Pike by uncalcified elastic rods in the pulp cavity. 



(2) By ankylosis, i.e. by the complete union of the cal- 

 cined tooth substance with the subjacent bone. This is the 

 commonest method among fish. 



