THE INCISORS. 



603 



of the tooth, in consequence of the double flattening of the latter. They are 

 similar in the incisors of both jaws. 



3d. Extremities. — The/ree extremitij is opposed to the corresponding tooth 

 of the other jaw, and should be examined first in the virgin tooth. 



Fig. 277.— Superior virgin incisor of the second dentition (pincer). 

 A. Anterior face. | B. Posterior face. | C. Profile. 



It is flattened from before to behind, and, consequently, elongated from side 

 to side. 



This extremity (Fig. 278) is occupied by a cavity called the external dental 

 cavity, c, which separates two borders, an anterior and a posterior ; two sides, an 

 external and an internal. 



These two borders are unequal. The anterior, a, is more prolonged and 

 more salient than the posterior ; it is thin, quite sharp, slightly convex trans- 

 versely, and is the first to appear in the eruption of the tooth from its alveolus ; 

 its pressure causes absorption and perforation of the gums. 



The posterior border, b, less salient than the anterior, sometimes has a 

 notch in its middle part, which renders the external dental cavity much less 

 regular. 



As to the sides, they constitute the commissures of the two borders ; the 

 external is thinner than the internal and presents a small notch. 



The external dental cavity or infundibulum, c, circumscribed by the central 

 enamel, d, has an irregularly conic form. Wider at its entrance than at its bot- 

 tom, and partially filled with cement, e, according to the sulijects (see Structure of 

 the Teeth), it is curved upon itself in its length, which draws its summit towards, 

 the posterior face of the tooth. 



According to Girard, whose remarks we have consulted, in horses six years 

 of age the external dental cavity of the inferior pincers has a depth of 0.016 to 

 0.018 m. ; that of the intermediates, 0.020 m. ; and that of the corners, 0.011 to 

 0.013 m. In the superior jaw its depth in the pincers is 0.025 to 0.027 m. ; in the 

 intermediates, 0.027 to 0.028 m. ; in the corners, 0.018 to 0.020 m. 



