840 On the Extinct Cats of America. > (December, 
remarked, the evidence of their possession of the characters of the 
Nimravide has not yet been obtained. There can be no reason- 
able doubt that the genera Drepanodon and Smilodon in the Fe- 
lide are the descendants of Hoplophoneus and allied genera. In 
fact, the Vimravide and Felide are “ homologous groups,” having 
corresponding terms in the manner I foreshadowed as a general 
principle in 1868 (Origin of Genera). 
In looking for causes in explanation of the modifications of 
structure cited, one can easily discover that there is a close rela- 
tion between the arrangement of the teeth and the mechanical 
laws involved in the performance of their function, those of seiz- 
ing an active prey, and of cutting up their carcasses into pieces 
suitable for swallowing. It is obvious that in the latter case the 
flesh teeth bear the resistance, and the masseter muscle is the 
power, and that the nearer these parts are together, the better is 
the function performed. As a matter of fact, the sectorial teeth in 
modern carnivora are placed exactly at the angle of the mouth, 
which is the front border of the masseter muscle. 
In the process of evolution both the muscle and the teeth have 
moved forwards in connection with the shortening of the jaw 
behind. This has been due to the necessity of bringing the power 
(masseter) nearer to another point of resistance, viz: the canine 
teeth. 
In the early carnivores (as Hyznodontide) the long jaws sup- 
ported more numerous teeth (#3) than in any modern families, 
and the fissure of the mouth was probably very wide, as the last 
molar was a sectorial. The canine teeth were evidently very inef- 
fective weapons. The animals probably only snapped with their 
jaws, and did not attempt to lacerate or hold on, as do the cats. 
he dogs of to-day are long jawed, and they snap in a manner 
quite distinct from anything seen among the cats. The only dogs 
that hold on are the short jawed bull-dogs. _ 
So in the use of the canines we have the ground of the short- 
ening of the jaw behind and before, and the consequent change of 
structure which resulted in the modern perfected Felide} 
The following list shows the number and distribution of the 
species of the Mimravide : ; 
‘See AMERICAN NATURALIST, 1878, p- 171. 
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