THE FAMILIES AND GENEKA 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 ErophyMa (Plates IX, X, fig. 2). 

 These differ from those of Phyllonycteris (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 MICROCHIROPTERA, p. 78. 



