FORMATION OF THE TEETH. 481 



formed edge of the tooth, and that results from the exact appo- 

 sition of the pulp and it. 



The crown or body of the tooth being finally finished, its 

 base is somewhat contracted, and thus forms the neck of the 

 tooth. In the subsequent process of the ossification of the roots, 

 the number of the latter is predetermined and always indicated 

 by the number of distinct vessels and nerves which go to the 

 pulp; there are, therefore, three roots to the upper molares, two 

 to the lower, one to the incisors, and so on. When the root is 

 fully formed, its extremity is tapered off to a conoidal point ; 

 and the canal or hollow in it containing the pulp is diminished 

 to a proportionate size, so that being also conoidal, its external 

 end appears as a very small opening not large enough to admit 

 a bristle. 



From the preceding account, it is clear that the bony part of 

 the tooth is formed by an exudation from the external surface 

 of the pulp; consequently, that the external lamina of the crown 

 is the first one deposited, and is originally of the size which it 

 ever afterwards retains; and that the pulp continues this secre- 

 tion of bony matter, from the circumference to the centre; until 

 the tooth, (body, neck, and root,) is completely formed. The 

 pulp, during this process, diminishes continually in size, but 

 elongates itself at the same time towards the bottom of the sock- 

 et; or, in the words of Mr. Hunter, " is lengthened into a fang." 



As the fang grows in length, the resistance being at its end, 

 causes the tooth to rise through the gum;. the socket, in the 

 mean time, has grasped the neck, or beginning fang, and, being 

 modelled upon the root, arises with it.* Mr. Hunter's experi- 

 ments on animals, interruptedly fed on madder, prove, conclu- 

 sively, that the bony part of a tooth is formed of lamellae, one 

 placed within another ; that the outer lamella being first formed, 

 is consequently, the shortest, and that the internal ones lengthen 

 successively. 



* The present doctrine about the dermoid origin of tlie teeth, seems to have pre- 

 sented itself forcibly to the original and sagacious mind of Mr. Hunter ; for he 

 says, "JBoth in the body and in the fang of a growing tooth, the extreme edge of 

 the ossification is so thin, transparent, and flexible, that it would appear to be 

 horny rather than bony, very much like the mouth or edge of the shell of a snail 

 when it is growing: and, indeed, it would seem to grow mueh in the same man- 

 ner, and the ossified part of a tooth would seem to have much the same connexion 

 with the pulp as a snail has with its shell/' Nat. Hist, of Human Teeth, p. 90, 



VOL. I. -41 



