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A MANUAL OF DENTAL ANATOMY. 



reversed part with those corresponding to them in the mole 

 or in Urotrichus. 



Speaking generally, it may be said that new cusps are 

 added to the number already existing, by the cingulum 



FIG. 121 



becoming elevated into points ; it is not very unusual to 

 see subsidiary cusps, obviously originating in this way, upon 

 human molars. 



Ridges may variously connect the cusps ; and the coales- 

 cence of two or more cusps to form an exceedingly elevated 

 point is illustrated by the Carnassial tooth of carnivora ; to 

 this transformation certain marsupial teeth form the clue, as 

 they afford unquestionable evidence of such coalescence by 

 a gradational series of small modifications in this direction 

 occurring in allied creatures. 



A simple pattern of tooth is formed by the junction of 

 the two anterior and two posterior cusps by simple ridges ; 

 and the cingulum may connect the outer ends of these two 

 ridges; such a tooth is seen in the Tapir and in the 

 Palseotherium. By the varied obliquity of these ridges, 



( x ) Upper molar teeth of (A) Urotrichus ; (B) Mole ; and (C) Chryso- 

 chloris. The four principal cusps are lettered a, &, c, d, in each of the 

 figures. In A the cingulum has been elevated so as to form four additional 

 cusps on the exterior of the tooth, and one additional cusp on the interior. 

 B and C show the fusion of certain of these cusps, and the consequent 

 diminution in their number. (From Mivart.) 



