72 THE PERMANENT 'DENTITION". 



There is a difference in the structure of all the teeth, 

 and an expert can tell to which socket each belongs. 

 They fit their sockets accurately,* are braced all round 

 by the jawbone processes, and receive besides support 

 and protection from the gums, which adhere to them 

 tenaciously and are almost as hard as cartilage. Use 

 and time, however, work changes, the teeth all wearing 

 down, the incisors in particular changing shape and 

 projecting outward. At the age of twelve years the 

 gums begin to slacken, causing the teeth to look 

 longer. The change from the upright position of the 

 incisors, and the increased space between them and 

 the canines, is caused by the elongation of the jaws, 

 which carries the incisors outward. The canines do 

 not change their position, but they become mere stubs. 



* " The manner of attachment of the human teeth is that 

 termed 'gomphosis/ i. e., an attachment comparable to the fit- 

 ting of a peg into a hole. The bony sockets, however, allow of 

 a considerable degree of motion, as may be seen by examining 

 the teeth in a dried skull, the fitting being in the fresh state 

 completed by the interposition of the dense periosteum of the 

 socket. This latter, by its elasticity, allows of a small degree 

 of motion in the tooth, and so doubtless diminishes the shock 

 which would be occasioned by mastication were the teeth per- 

 fectly immovable and without a yielding lining within their 

 sockets." C. S. Tomes, "Dental Anatomy" &c., p. 23. 



John Hunter says (" Human Teeth ") : " The roots of the 

 teeth are fixed in the gum and alveolar processes by that species 

 of articulation called gomphosis, which in some measure resem- 

 bles a nail driven into a piece of wood. They are not, however, 

 firmly united with the processes, for every tooth has some de- 

 gree of motion ; and in heads which have been boiled or macer- 

 ated in water, so as to destroy the periosteum and adhesion of 

 the teeth, we find them so loosely connected with their sockets 

 that the incisors are ready to drop out, the grinders remaining, 

 8 it were, hooked, from the number and shape of their roots. " 



