A MONOGRAPH OF THE BATS OF NORTH AMERICA. 27 



The toes retain two phalanges to tlie first toe; all the others have 

 three, but differ in their relative lengtlis. The first phalanx of the first 

 toe is, so tar as examined, longer than that of tlie other toes. In 

 rterojyus tlie lengths of the toes from the second to the fifth gradually 

 diminish. In Chilonycteris they abruptly increase, that of the second 

 toe being one-third shorter than the fifth. In all bats the tarsus and 

 calcaneum are elongate and exhibit the general character of these bones 

 in mammals, in which little or no weight is borne upon the posterior 

 extremities. Both bones are so disposed that the larger end of each is 

 directed proximally. In Bhinolophus the calcaneum enters into the 

 ankle joint. In other forms the calcaneum is independent of the joint. 

 In Phyllostomida', including Xataln.s, as well as in the gcuns Iihyncho- 

 nycteris, the calcar* is placed in axial line with the calcaneum. In 

 other families it joins the calcaneum to its outer side at a well-defined 

 angle. As a rule the astragalus and calcaneum are nearly of one size, 

 but in the genus last named the calcaneum is notably the smaller (Am. 

 Naturalist, Feb., 1886, 170). 



GENERAL PLAN OF ANTERIOR EXTREMITIES IN FLYING VERTE- 



BEATED ANENIALS. 



From tlie above consideration it will be seen that the wing mem- 

 branes possess various features which can be used in distingnishing 

 the members of the order. But after what manner are the flying mam- 

 mals distinguished from other flying vertebrates? 



There are two distinct types of modification which the vertebrate 

 skeleton has undergone in adapting the animal for flight, both of which 

 depend upon some peculiarity in the structure of the anterior extremi- 

 ties; and in order to obtain a correct opinion of them we propose to 

 cast a glance at each in turn. 



A plan of 1)0 nil -slrKcture of the iviiif/.s of Jliiin// rcrlebrotr animals. 



a. Bones of carpus nnunited 

 distinct; lUfi^lit main- 

 tained by dermal ex- 

 panse. 



1). Bones of carpus united 

 flight maintained by ) 

 dermal appendages, 



I. Wing membrane supported by all fingers. 



Bats (VespertilioX. order of Mammalia. 

 II. Wing membrane supported by the fourth finger 

 only (wliich is immensely developed), the 

 others remaining free. 



rtcrodacfi/les, order of Keptilia. 

 rlll. Boiu>s of metacarpus, two to three in number; 

 feathers not radiating. 



Lirhit/ birds (Aats) — class. 

 IV. Bones of metacar])us, lour in number; feathers 

 radiating. 



Archaopiiryx (AvE.s) — subclass. 



*The calcar is an element of doubtful homology. It supports the free border of 

 the interfemoral membranr and is of tbc same signilicauce as the accessory carti- 

 lage of the fifth manal digit. 



