THE FAMILIES AND GENERA OF BATS. 
43 
From such teeth as those of Rhinophylla to the excessively modi- 
fied molars of the Desmodontida; (Plates IX and X, fig. 3) the tran- 
sition could readily be made. The cutting edge in these minute teeth 
therefore probably represents the combined paracone and metacone in 
the maxillary teeth and the protoconid and hypoconid in the lower 
jaw. It is useless, however, to attempt to suggest exact homologies 
for the three cusps indicated in the posterior lower cheek tooth of 
Desmodus , as it is probable that these are mere secondary growths. 
Another suggestion as to the probable origin of the Desmodontine 
molars is furnished by the teeth of Erophylla (Plates IX, X, fig. 2). 
These differ from those of PhyZlonycteris (Plates III, IV, fig. 4) in 
their distinct narrowing and in the development of a well-defined cut- 
ting edge along the outer portion of the crowns, both above and below. 
Order CHIROPTERA. 
1779. Chiroptera Blumenbach, Handbuch der Naturgeschichte, p. 74. 
Geographic distribution. — Eastern and western hemispheres to the 
northern and southern limits of tree growth. In the Pacific Ocean 
the range of the order extends to the Galapagos Islands and Hawaii 
from America, and to New Zealand, Samoa, the Caroline and Ladrone 
Islands from Asia. 
Characters. — Mammals with the front limbs modified for true 
flight, the fingers greatly elongated (the third usually at least equal 
to head and body) and joined together by a membrane which extends 
to sides of body and legs ; shoulder girdle much more developed than 
pelvis, the sternum usually keeled ; knee directed backward owing to 
rotation of leg for support of wing membrane. 
Number of forms. — There are at present recognized about 900 
forms of Chiroptera, a number probably representing considerably 
less than half of what will eventually be known. 
Principal subdivisions. — The families of bats fall naturally into 
two main groups representing, as Winge has shown, two distinct 
stages in the specialization of the anterior limbs for flight. They 
may be distinguished as follows: 
KEY TO THE SUBORDERS OF CHIROPTERA. 
Second finger retaining an evident degree of independence, its ungual pha- 
lanx present; humerus with trochiter and trochin small, the former 
never articulating with the scapula ; mandible with angular process 
broad and low or practically absent ; margin of ear forming a com- 
plete ring MEGACHIROPTERA, p. 44. 
Second finger scarcely if at all independent from third, its ungual phalanx 
absent ; humerus with trochiter and trochin large, the former usually 
articulating with the scapula ; mandible with angular process well 
developed, long and narrow ; margin of ear not forming a complete 
ring MICROCHIRORTERA, p. 78. 
