202 A MANUAL OF DENTAL ANATOMY. 



THE ATTACHMENT OF TEETH. 



Although the various methods by which teeth are fixed in 

 their position upon the bones which carry them pass by 

 gradational forms into one another, so that a simple and at 

 the same time absolutely correct classification is impossible, 

 yet for the purposes of description four principal methods 

 may be enumerated, namely, attachment by means of fibrous 

 membrane, by a hinge, by anchylosis, and by implantation 

 in bony sockets. 



Attachment by means of Fibrous Membrane. An" 

 excellent illustration of this manner of implantation is 

 afforded by the Sharks and Rays, in which the teeth have 

 no direct connection with the cartilaginous, more or less 

 calcified, jaws, but are imbedded solely in the tough fibrous 

 mucous membrane which covers them. This, carrying with 

 it the teeth, makes a sort of sliding progress over the curved 

 surface of the jaw, so that the teeth once situated at the 

 inner and lower border of the jaw, where fresh ones are 

 constantly being developed, rotate over it, and come to 

 occupy the topmost position (cf. description of the denti- 

 tion of the sharks). That the whole fibrous gum, with the 

 attached teeth, does really so slide over the surface of the 

 jaw, was accidentally demonstrated by the result of an injury, 

 which had been inflicted upon the jaws of a shark. 



The fibrous bands by which each individual tooth of the 

 shark is bound down are merely portions of that same sheet 

 of mucous membrane which furnished the dentine papillae ; 

 and the gradual assumption of the fibrillated structure by 

 that portion of the mucous membrane which is contiguous 

 to the base of the dentine papilla may be traced, no such 

 fibrous tissue being found at the base of young papillae, and 

 very dense bands being attached to the bases of the com- 

 pleted calcified teeth. 



Attachment by an Elastic Hinge. The possession 



