468 



SPECIAL HISTOLOGY. 



bone, and in other respects clearly allied to it, must, from their develop- 

 ment, be regarded as modifications of the mucous membrane. 



In every tooth we must distinguish the tooth proper, and the soft 

 structures; the former consists of a free part, the crown, and of an im- 

 bedded portion, the simple or multiple fangs, whose special forms are 

 treated of in anatomical works ; they contain internally a small cavity, 

 the pulp cavity, which extends through each fang as an elongated canal 

 opening at its point by a simple, or more rarely double (Havers, Rasch- 

 kow) fine aperture. 



Among the soft parts we may enumerate first, the gum, gingiva, a 

 dense mass formed by the union of .the mucous membrane and of the 

 periosteum of the jaw, which surrounds the lower half of the crown or 

 the neck of the tooth. Secondly, the periosteum of the alveolus, which 



Fig 183. 



unites the tooth very closely with 

 the alveolus. Finally, the pulp, a 

 soft, vascular and nervous mass, 

 which occupies the cavity of the 

 tooth, and is connected with the 

 periosteum of the alveolus, through 

 the aperture in the fang. 



The proper tooth (Fig. 183) con- 

 sists of three distinct structures. 

 1. The dentine, which constitutes its principal mass, and determines its 

 general form. 2. The enamel, which forms a tolerably thick invest- 

 ment to the crown ; and 3. The cement, which covers the fang exter- 

 nally. 



138. The dentine or ivory (Fig. 183, d), is yellowish-white and 

 translucent or transparent, in thin sections of a recent tooth ; when dry 

 it has a silky or satiny aspect, in consequence of the reception of air 

 into a special system of canals. It is considerably harder and more 



FiG. 183. Molar tooth (human) ; magnified about 5 diameters: 1, longitudinal ; 2, trans- 

 verse section: a, enamel; 6, pulp cavity; c, cement; d, dentine, with its canals. 



