116 THE VITAL FUNCTIONS. 



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

 same proportion encroaching upon the cavity occupied by 

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

 small compass, and fills 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 disappears. But the formation 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 

 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 quadrupeds, 

 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. But his brother, M. Frederic Cuvier, 



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



