392 
Miscellaneous. 
not been subjected to it, are reduced like those of the superior 
sectorial, which have. Indeed it is possible that some ot' the Creo- 
donta, the carnivores of the lower Eocene, may have been derived 
from ancestors without or with rudimental inner cusps. In any 
case the effect of use in lengthening the cusps appears to have 
operated in the Carnivora, as it has done to a greater degree in the 
Ungulata; and the lateral vertical wear would appear to have re¬ 
sulted in the blade-form, as transverse wear in the Ungulates has 
resulted in the plane grinding surface. 
The specialization of one tooth to the exclusion of others as a 
sectorial, appears to be due to the following causes. It is to be 
observed, in the first place, that when a carnivore devours a carcass, 
it cuts off masses with its sectorials, using them as shears. In so 
doing it brings the part to be divided to the angle or canthus of 
the soft walls of the mouth, which is at the front of the massetor 
muscle. At this point the greatest amount of force is gained, since 
the weight is thus brought immediately to the power, which would 
not be the case were the sectorial situated much in front of the 
masseter. On the other hand, the sectorial could not be situated 
further back, since it would then be inaccessible to a carcass or mass 
too large to be taken into the mouth. 
The position of the sectorial tooth being thus shown to be depen¬ 
dent on that of the masseter muscle, it remains to ascertain a pro¬ 
bable cause for the relation of the latter to the dental series in 
modern Carnivora. Why, for instance, were not the last molars 
modified into sectorial teeth in these animals, as in the extinct 
Jlyainoclon and various Creodonta ? The answer obviously is to bo 
found in the development of the prehensile character of the canine 
teeth. It is probable that the gape of the mouth in the Hyceno- 
dons was very wide, since the masseter was situated relatively far 
posteriorly. In such an animal the anterior parts of the jaws with 
the canines had little prehensile power, as their form and anterior 
direction also indicates. They doubtless snapped rather than lace¬ 
rated their enemies. The same habit is seen in the existing dogs, 
whose long jaws do not permit the lacerating power of the canines 
of the Felidae, though more effective in this respect than those of the 
Hyamodons. 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 anterior the position of the masseter muscle, 
the more effective the canine teeth. Hence it appears that the 
relation of this muscle to the inferior dental series depended origi¬ 
nally on the use of the canines as prehensile and lacerating organs, 
and that its 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 below, have become specialized 
as sectorials, while the fifth, sixth, and seventh have, first, re¬ 
mained tubercular as in the dogs, or, secondly, have been lost, as 
in by am as and cats .—American Naturalist, March 1879. 
