THE FAMILIES AND GENERA OF BATS. 
35 
the upper tooth. As the jaws close the cutting edges pass each other 
with a shearing motion, c 1 working against posterior edge of pm 4 , c 2 
against c 1 , c 3 against c 2 , c 4 against c 3 , and so on to the end of the 
series. At the same time a less important though equally definite 
action takes place between the innermost cusps of both sets of teeth. 
This consists principally of the passing of the posterior inner side 
of mcd 1, 2, and 3 and anterior inner side of ecd 1, 2, and 3 across 
the inner surface of the three protocones, the point of the large cusp 
in each instance fitting closely to the angle between the two small 
ones. The paraconid of m 2 and m 3 also comes within cutting dis- 
tance of the hypocone of m 1 and m 2 when it is large enough to be 
functional. As the stroke finishes each hypoconid scrapes through 
the hollow at middle of opposed crown, and finally comes in oppo- 
sition with inner side of corresponding protocone, across which it 
passes as the jaw is moved downward and toward the opposite side 
to take its position for the next stroke. At the same time each 
protoconid passes through the space at front of its corresponding 
upper tooth and comes similarly in opposition with posterior heel 
of the tooth in front, or with its hypocone when this cusp is present. 
While the full stroke just described is taking place on one side, a 
somewhat reversed half stroke occurs on the other, the inner surface 
of the long outer cusps of the lower teeth cutting against the outer 
side of the opposed inner cusps of the upper teeth, the action between 
them being the exact reverse to that which takes place near the end 
of the full stroke. As the recovery for the next stroke proceeds, 
the rounded convex outer surface of the protoconids and hypoeonids 
pass through the depressions between the paracones and metacones, 
while the similarly rounded inner surfaces of the upper teeth pass 
between the main cusps of the lower teeth, the result being a grind- 
ing and crushing action which must be very effective in the final 
trituration of small particles of food. 
The foregoing description of the' molars in action is primarily based 
on the genus Noctilio , in which the molars are large enough to be 
readily examined and in which their effectiveness of structure is at 
its maximum. The cutting apparatus is essentially the same in all 
bats with normal teeth, though its apparent effectiveness is in some 
instances reduced without any considerable change in the form of the 
cusps. Thus, in Myotis myotis the protoconids and hypoeonids are 
so long and straight that they are less readily brought in contact with 
the styles, the stroke apparently losing thereby. In some Phyllosto- 
midse the lateral motion of the mandible is lessened by the large size 
of the canines, which in certain genera develop large cutting edges. 
When this occurs the outer portion of the upper molars appears to be 
invariably reduced, the corresponding change in the lower teeth 
showing itself in the lessened transverse diameter of the triangles. 
