22 



AGE OF THE DOMESTIC ANIMALS. 



The other, which forms the ivory or dentine, remains until 

 a more or less advanced period of the life of tlie animal, and 

 furnishes the tooth witli its vitality. 



In the interspace between these two papillary systems 

 is deposited the matter which constitutes the bulk of the tootli 

 (Fig. 11, d). This at first consists of a very thin, conical plate 

 hollowed out on the inside, and containhig a deep depression 



on its free extremity. Later, 

 the walls of the dental fol- 

 licle (Fig. 11, c) are trans- 

 formed into the alveolar 

 periosteum. If we refer now 

 from Fig. 11, where we find 

 a, the papilla of the enamel; 

 h, the papilla of the ivory ; 

 d, the plate consisting of the 

 deposits of these two papillae, 

 — that is, the enamel and 

 dentine juxtaposited, — and 

 c, the germ sac, which is to 

 become the alveolar perios- 

 teum, to Fig. 12, which is a 

 longitudinal antero-posterior 

 section of an inferior perma- 

 nent pincher tooth, fully 

 developed (somewhat en- 

 larged), we find E, the 

 enamel of the cup, surround- 

 ing this cavity, from which the papilla has entirely disappeared ; 

 P, the cavity of the ivory papilla very much diminished in 

 size ; 7, the dentine occupying the major portion of the tooth, 

 having developed on the inner surflice of the thin plate which 

 we found in Fig. 11. In Fig. 12, at T, which represents the 

 table of the tooth after the borders have been worn, we find a 

 separation of the enamel of the cup and the ivory enamel (Fig. 

 12, E E)^ which we find continuous in Fig. 11, dd. 



Fig. 11. 

 Schematic section of the dental follicle of an 

 inferior incisor in the horse, a, sui)erior papilla, — 

 germ of the enamel ; b, inferior papilla, — dental 

 pulp or germ of the ivory ; c, wall of the follicle; 

 d, plate of enamel and dentine juxtaposited. 



