30G 



THE TEETH. 



central incisors, the other teeth of the upper jaw are thrown somewhat 

 outwards, so that in closure of the jaws the canines and bicuspids come 

 into contact partly with the corresponding lower teeth, and partly with 

 those next following ; and in the case of the molars, each cusp of the 

 upper lies behind the corresponding cusp of the lower teeth. Since, 

 however, the upper molars and especially the wisdom-teeth are smaller 

 than those below, the dental ranges terminate behind nearly at the 

 same point in both jaws. 



The MiriK-TERTH(fig. 20G). — The temporary incisor and canine teeth 

 resemble those of the permanent set in their general form ; but they 

 are of smaller dimensions. The temporary molar teeth present some 

 peculiarities. The hinder of the two is much the larger ; it is the 

 largest of all the milk-teeth, and is larger even than the second per- 

 manent bicuspid, which it afterwards gives place to. The first upper 

 milk molar has only three cusps, two external and one internal ; the 

 second has four. The first lower temporary molar has four cusps, and 

 the second five, of which in the latter case three are external. The 



Fig. 206. 



Fig. 206. — Milk Teeth of the Right Side ov the TJprEr. and Lower Jaws. 

 a, the incisors ; h, tlie canines ; c, tlie molar teetli. 



fcoif/s of the temporary molars resemble those of the permanent set, but 

 they are smaller, and are more divergent from the neck of the tooth. 



STRUCTURE OF THE TEETH. 



On making a section of a tooth, the hard substance of which it is 

 composed is found to be hollow within (fig. 207). The form of tlie 

 cavity bears a general resemblance to that of the tooth itself ; it 

 occupies the interior of the crown, is widest opposite to or a little 

 above the neck, and extends down each fang, at the point of which 

 it opens by a small orifice. In the incisor teeth the cavity is prolonged 

 above into two fine linear canals, which proceed one to each corner of 

 the cvown ; in the bicuspid and molar teeth it advances a short 

 distance into each cusp. In the case of a root formed by the blending 

 of two or more fangs, as occurs occasionally in the wisdom-teeth, each 

 division has a separate canal prolonged down to its apex. 



Pxilp of the teeth. — The central cavity of a tooth is called the 

 pdj) cavity, because it is occupied and accurately filled by a soft, highly 



