THE TEETH 



411 



The crown is a cutting blade which forms with the lower molar a 

 scissors-like shearing apparatus ; hence both these teeth are termed the 

 sectorial, 1 or carnassial, 2 teeth. 



The cutting blade of the upper sectorial is composed of a principal 

 cusp, or protocone, and a greatly enlarged posterior basal cusp, or 

 tritocone, which is separated from the principal cusp on the outer side 

 by a narrow vertical cleft and on the inner surface by a deep excava- 

 tion. It presents a sharp horizontal cutting edge, which begins behind 

 at the prominent posterior end of the cingulum and is directed forward 

 and inward to the point of the principal cusp, whence it is continued 

 upward and outward as a sharp anterior border. The inner surface of 

 the two cusps is flat or slightly convex from before backward, and 

 shears against the outer surface of the lower sectorial. The outer 

 surface of the posterior basal cusp is slightly concave, and slopes 

 downward and inward. The outer surface of the principal cusp is 

 strongly convex antero-posteriorly. 



The broad anterior part of the crown is occupied by two small 

 conical cusps. Of these, the outer and smaller, the anterior basal cusp 

 or protostyle, is connected with the anterior border of the cutting blade 

 and is supported by the anterior outer fang. The inner and larger cusp, 

 the deuterocone, is distinct, and supported by the larger inner fang. 



The anterior fangs are directed upward parallel with each other. 

 When the tooth is in the jaw the outer fang is in advance of the 

 inner. Both are oval in transverse section, but are placed at such an 



Posterior Cusp. 

 Inner Cusp. 



Inner Fang. 



Outer Cusp. 

 Neck. 



Outer Fang 



FIG. 328. 



Posterior Cusp. 



Inner Cusp. 



Inner Fang. 



Anterior 

 Ridge. 



Outer Side 



Groove. 



Inner Side. 



ANTERIOR ASPECT. 



POSTERIOR ASPECT. 

 RIGHT UPPER MOLAR TOOTH. 



Posterior Cusp. 

 INFERIOR ASPECT. 



angle to each other that the long diameters of the ovals if produced 

 would meet behind under the middle of the crown. 



The posterior triangular fang is strongly flattened from side to side, 

 and carries the protocone and the tritocone. The cingulum is well 

 marked and strongly curved toward the crown behind. 



1 From secare, sectum, to cut. 2 From caro, carnis, flesh. 



