58 THE PERMAN^EXT DEKTITIOX. 



central enamel, &c., according to Surgeon J. Hughes's 

 measurements, penetrates the lower centrals to the 

 depth of from -| to -^^ of an inch ; the divid- 

 ers from yV to f, and the corners from -| to 

 f. It penetrates the upper centrals from 1 

 inch and -^^ to 1 and ^ ; the dividers from 

 1 and I to 1 and J, and the corners from | 

 to nearly 1 iuch. Prof. Youatt says the 

 grinders have each two infundibula, which 

 penetrate to their roots. 



The following is Prof. A. Chauveau's description of 

 the incisor teeth ("The Comparative Anatomy of the 

 Domesticated Animals/^ Fleming's trans., p. 349) : 



"The general form of the incisors is that of a tri- 

 faced pyramid, presenting an incurvation whose con- 

 cavity is toward the mouth. Tlie base of this pyra- 

 mid, the crown of the tooth, is flattened before and 

 behind. The summit or extremity of the fang, is, on 

 the contrary, depressed on both sides. The shaft of 

 the pyramid presents at different points of its hight, a 

 series of intermediate conformations, which are utilized 

 as indications of age, the continual growth of the teeth 

 bringing each of them in succession to the frictional 

 surface of the crown. 



" Examined in a 3^oung tooth, but one that has com- 

 pleted its evolution, the free portion presents the fol- 

 lowing characteristics: An anterior face, indented by 

 a slight longitudinal groove, which is prolonged to 

 the root ; a posterior face, rounded from side to side; 

 two borders, of which the internal is always thicker 

 than the external; and, lastly, the surface of friction. 

 The latter does not exist in a tooth that has not been 

 used, but in its stead are two sharp margins, circum- 



