No. 2. ] THE HARD PARTS OF THE MAMMALIA. 235 
mouth in the Hyznodons was very wide, since the masseter was 
situated relatively far posteriorly. In such an animal the ante- 
rior parts of the jaws with the canines had little prehensile 
power, as their form and anterior direction also indicates. They 
doubtless snapped rather than lacerated their enemies. The 
same habit is seen in 
the existing dogs, 
whose long jaws do 
not permit the lacera- 
ting power of the ca- 
nines of the Felidz, 
though more effective 
in this respect than 
those of the Hyzno- 
dons. The usefulness 
of a lever of the third 
kind depends on the 
approximation of the 
power to the weight ; 
that is, in the present 
case, the more ante- 
rior the position of 
the masseter muscle, 
the more effective the 
canine teeth. Hence 
it appears that the re- 
lation of this muscle 
to the inferior dental 
series depended origi- 
Figure 61.— Smilodon neogeus Yund; skull right side; from the Pampean epoch 
of Buenos Ayres; original; much reduced. 
nally on the use of the canines as prehensile and lacerating 
organs, and that its relative insertion has advanced from behind 
forwards in the history of carnivorous types. Thus it is that 
the only accessible molars, the fourth above and the fifth 
