116 THE VITAL FUNCTIONS. 



deposited, and building up the body of the tooth, and in the 

 same projiortion cncroachinii; upon tlie cavity occupied by 

 the pulp, which retires before it, until it is shrunk into a 

 small compass, and fdls only the small cavity which remains 

 in the centre of the tooth. The ivory has by this time re- 

 ceived from the capsule a complete coating of enamel, which 

 constitutes the whole outer surface of the crown; after which 

 no more is deposited, and the function of the capsule having 

 ceased, it shrivels and disaj^pears. But the formation of 

 ivory still continuing at the part most remote from the 

 crown, the fangs are gi'adually formed by a similar process 

 from the pulp; and a pressure being thereby directed against 

 the bono of the socket at the part where it is the thinnest, 

 that portion of the jaw is absorbed, and the ])rogress of the 

 tooth is onl}^ 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 

 is beautifully illustrated by feeding a young animal at dif- 

 ferent times with madder; the teeth which are formed at 

 that period exhibiting, in consequence, alternate layers of 

 red and of white ivory.* 



/ The formation of the teeth of herbivorous quadruj:)eds, 

 which have three kinds of substance, is conducted in a still 

 more artificial and complicated manner. Thus, in the ele- 

 phant, the pulp which deposites the ivory is extended in the 

 form of a number of parallel plates; while the capsule which 

 invests it, accompanies it in all its parts, sending down du- 

 plicatures of membrane in the intervals between the plates. 

 Hence the ivory constructed by the pulp, and the enamel 

 deposited over it, are variously intermixed; but besides this, 

 the crusta petrosa is deposited on the outside of the enamel. 

 Cuvier asserts that this deposition is made by the same cap- 

 sule which has formed the enamel, and which, previously 

 to this change of function, has become more spongy and 

 vascular than before. Hut his brother, M. Frederic Cuvier, 



• Cuvier. Dictionnnirc dcs Sciences Medicalcs, t. viii. p. 320. 



