410 



MAMMALIAN ANATOMY 



The second upper premolar (Fig. 326) resembles the second lower 

 premolar already described ; the small anterior cusp of the crown is 

 usually wanting, and, when present, is an inconspicuous elevation of 

 the inner anterior end of the cingulum. The principal cusp, or proto- 

 cone, and the posterior basal cusp, or tritocone, are distinct. The outer 

 surface of the crown is that one which is strongly convex from before 

 backward, and marked by the median vertical ridge. The inner sur- 

 face is natter, and its posterior part, which shears against the anterior 

 part of the outer surface of the second lower premolar, often exhibits 

 evidence of wear. The borders are directed toward the inner side of 

 the ends of the base. The cingulum is swollen on the inside behind 

 the middle, and sometimes presents at this point a distinct cusp, or 

 deuterocone, borne on a separate slender inner fang. The posterior 

 fang is much stronger than the anterior, and is prismatic on cross- 



FIG. 327. 



Principal Cusp. 



Cingu- 

 lum. 



Posterior 

 Fang. 



Anterior Basal Cusp 



Anterior Outer Fang 

 Inner Fang. 



Cingu- 

 lum. 



Posterior 

 Fang. 



INNER ASPECT. 



OUTER ASPECT. 



fimer Cusp. 



Anterior Basal 

 Cusp. 



Principal 

 Cusp. 



Posterior 

 Basal Cusp. 



INFERIOR ASPECT. 

 RIGHT THIRD UPPER PREMOLAR TOOTH. 



section, because in addition to the outer and inner surfaces it presents 

 opposite the anterior fang a third narrow and deeply grooved surface, 

 which faces outward and forward ; the inner surface often exhibits a 

 wide vertical groove. 



The third upper premolar (Fig. 327) is twice as large as the second 

 premolar. Its broader anterior end has two transversely placed fangs ; 

 the greater part, however, is supported by a single large posterior fang. 



