DENTITION. 141 



tooth. The thin scales of ivory thus formed in- 

 crease by further depositions made in the cells at 

 the surface of the pulp, till the whole has formed 

 the first, or outer layer of ivory : in the mean time, 

 the inner surface of the capsule, which is in imme- 

 diate contact with this layer, secretes the substance 

 that is to compose the enamel, and deposits it in 

 the cells contiguous to the ivory. This double 

 operation proceeds step by step ; fresh layers of 

 ivory being formed, and thus building up the body 

 of the tooth, into which the outer portion of the 

 pulp is converted ; and only the remaining portion 

 fills up the small cavity which remains in the centre 

 of the tooth. The ivory has by this time received 

 from the capsule a complete coating of enamel, 

 which constitutes the wdiole outer surface of the 

 crown ; after which no more calcareous matter is 

 deposited ; and the function of the capsule having 

 ceased, it shrivels and disappears. But the for- 

 mation of ivory still continuing at the part most 

 remote from the crown, the fangs are gradually 

 formed by a similar process from the pulp ; and a 

 pressure being thereby directed against the bone of 

 the socket, at the part where it is the thinnest, that 

 portion of the jaw is absorbed, and the progress of 

 the tooth is only resisted by the gum ; and the gum, 

 in its turn, soon yielding to the increasing pressure, 

 the tooth cuts its way to the surface. This process 

 of successive deposition and formation is beautifully 

 illustrated by feeding a young animal at ditterent 

 times with madder ; the teeth which are formed at 

 that period exhibiting, in consequence, alternate 

 layers of red and of white ivory.* 



* Cuvier. Dictionnaire des Sciences Medicales, t. viii. p. 320. 



