360 MICROSCOPIC ANATOMY OF THE TEETH 



It would thus appear that the posterior hinge consists of two 

 different substances an outer stiffened portion which is 

 possessed of considerable rigidity but great elasticity, and 

 an inner fibrous portion made up of strands of fibres of an 

 elastic nature, which become relaxed when the tooth is 

 pushed backwards and straighten out when the pressure is 

 removed, and with the stiffer arched spring-like portion at 

 the back immediately return it to its position on the bone. 



FIG. 239. The posterior hinge of the tooth of the Hake (Merluccius). 

 d. Calcified portion of the tooth inverted into the fibrous portion of the 

 hinge/. ; s. stiffened elastic part of posterior hinge ; p. pulp of the tooth. 



(x 150.) 



In fig. 239 the fibrous portion of the hinge is shown under 

 higher magnification and its attachment to the prolonged 

 portion of the vasodentine (d). These fibres, when teased 

 out in glycerine or water, curl very much in the same manner 

 as those of ordinary elastic tissue. 



The anterior hinge, as shown in Plate VI B and fig. 238, a, is 

 divided into two portions, the tooth in the centre lying free 

 on the bony pedestal. 



This hinge is made up of stout fibres, which are inserted 

 into the tooth above and the bone below. It is of consider- 

 able thickness and stains blue like the fibrous portion of the 



