No. 2.] THE HARD PARTS OF THE MAMMALIA. 231 
size of the teeth. In the opening of the jaws in a Creodont, 
the elevated portion of the inferior crown shears by its posterior 
face against the anterior face of the superior molar, thus re- 
Figure 56.— Centetes ecaudatus: A, skull, side seen obliquely from below; A; 
superior molars from below; C, inferior molars from above. 
straining its extension posteriorly. The stimulus of use, how- 
ever, develops a low extension posteriorly, or a heel, which cov- 
ers the posterior root, and opposes in mastication the internal 
extremity or tubercle of the crown of the superior molar above it. 
Thus a molar element in mastication is added to the sectorial in 
some Creodonta, and in Canidz and Urside, etc., among Car- 
nivora. This function predominates over that of the anterior 
triangle in the Lemuridz (Fig. 57). 
ZT 
eZ 
Y ff 
U) ; 
i Hi Mi ( 
Figure 57.— Lemur collaris, dentition closed, showing development of heel of 
inferior molars; original. 
