222 COPE. [Vot. III. 
7. ORIGIN OF THE SECTORIAL DENTITION. 
The successive modifications of form which have resulted in 
the existing specialized single inferior sectorial tooth of the 
Felidae have been already pointed out. They have been shown 
to consist in the gradual obliteration of the internal and poste- 
rior tubercles, and the enlargement of the two external tubercles 
of the primitive triangle, together with the extinction of the 
heel. The modification in the character of the dentition taken 
as a whole was shown to consist in the reduction of the num- 
ber of the teeth, including the sectorials, until in Felis, etc., we 
have almost the entire function of the molar series confined © 
to a single large sectorial in each jaw. 
The genesis of the superior sectorial tooth has been explained 
as follows. In consequence of the fact that the lower canine 
tooth shuts anterior to the superior canine, the result of the 
enlargement of the diameters of those teeth will be to cause 
the crowns of the inferior teeth to be drawn from behind for- 
wards against those of the superior teeth (Fig. 58). Thus a 
shearing motion would result between the anterior external edge 
of the lower triangle and the posterior internal edge of the 
Figure 58.— Stypolophus whitie Cope; diagram representing the apposition of 
the inferior and superior molars. The superior are in light, the inferior in heavy 
lines. The numbers represent the molars and premolars: C. canine; foc. proto- 
cone; fac. paracone; mc.metacone; POC. protoconid; PAC. paraconid; A/C. meta- 
conid; 4c. hypocone; A/C. hypoconid. 
superior triangle. Now the characters of the true sectorial teeth 
consist in the enormous extension of these same edges in a fore 
and aft direction, the inferior shutting inside of the superior. 
To account for the development of these blades we must under- 
stand that the oblique pressure of the front edge of the lower 
tooth, on the hind edge of the superior tooth, has been continued 
