LESSON 56.] THE STRUCTURE OF THE TEETH. 



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849. A figure (322) of a longitudinal section of the incisor of a 

 Rabbit is given. he enamel (a) forms a chisel-shaped cutting 

 instrument at the apex of the tooth ; within the point, the crusta 

 petrosa (&) forms a very delicate line, which is continued along the 

 inner surface of the tooth ; within this tissue, and the enamel, is the 

 dentine (c), and in the centre of it, the pulp cavity (d). 



850. A transverse section of such a tooth (Fig. 323) is very in- 



FIG. 322. 



FIG. 323. 



Transverse section, Incisor, Kabbit. 



Longitudinal section, Incisor, Rabbit- 



structive ; it is somewhat triangular in shape, the front being par- 

 ticularly flat, while the sides recede, and are rounded at the back. 

 The enamel (a) occupies the entire front, and for its security em- 

 braces the corners, and is gradually lost at the sides ; here the crusta 

 petrosa (b) begins, and completes the outer wall of the tooth. As in 

 the former illustrations, within these tissues is the dentine (c) , and 

 in the centre the pulp cavity (d). 



851. As far as the alternation of tissues is concerned, the molar 

 teeth of the Rodents are formed on the same plan as those of the 

 herbivorous quadru- 

 ped, the arrangement 



being, however, some- 

 what different. 



852. A figure of a 

 Rabbit's molar tooth 

 is given in Fig. 324. 

 In preparing 'these 

 teeth, they almost in- 

 variably break into Transverse section of Molar tooth, Eabbit. 



four pieces, in consequence of the brittleness of the crusta petrosa, 



FIG. 324. 



