THE TEETH 



439 



lacks this fifth cusp. The first two lower molars have two fangs, but 

 in the third the two fangs are more or less coalesced. 



The upper molars have the crowns more regularly cuboidal, and 

 elevated into four cusps, one at each angle. The third molar often 

 presents only three cusps, as does sometimes the second molar also, 

 through the failure of the posterior-internal to develop. When there 

 are four cusps the anterior-internal is the largest and curves outward 

 in front and behind to join the external cusps, while the posterior- 

 external cusp curves inward to join the posterior-internal. The 

 elevated part of the triturating surface of the quadritubercular crown 

 is therefore S-shaped, beginning on the outside with the anterior- 

 external cusp and winding inward, then outward, and then inward 

 again to end with the posterior-internal cusp. 



The upper molars normally have three fangs, two external and 

 vertical, and one internal larger and directed upward and inward. 

 The last upper molar, however, often has only a single fang. 



The deciduous teeth (Fig. 369) number twenty, distributed as 



212 



follows : di > dc -> dm - The incisors and canines resemble the 







permanent teeth, but are relatively broader, with fangs not laterally 



FIG. 369. 



123 45 



67 89 



THE TEMPORARY TEETH OF ONE SIDE. 



1, 2, upper and lower iucisors ; 3, upper and lower canine ; 4, 5, upper and lower molars ; (i, 7, triturating surface 

 of the lower molars; 8, 9, triturating surface of the upper molars. 



compressed. The molars are formed on the same general pattern as 

 the permanent molars ; their crowns are shorter, however, and their 

 fangs more divergent. The crown of the first upper molar sometimes 

 resembles the crown of a premolar. 



