4 BULLETIN 43, UNITED STATES NATIONAL MUSEUM. 



The digits on their palmar aspect may be sharply defined as in the 

 Phyllostomida. and Corijnorhinm, or they may be obscured by the mem- 

 brane or the upper part in the forepart of the hand, namely, in the 

 region of the second, third, and fourth digits, as in Molossi, Vesperti- 

 lionuUB and the genus Antrozous. The membrane may lie chiefly on 

 the upper aspect of the digits, as in most bats, or at the lower That 

 m tlie second interspace may bo attached to the upper border of the 

 second and to the lower border of the third metacar])al bone. 



Tlie skin is nnich more loose about the legs than tlie arms and on tlie 

 mterfemoral membrane than the wing membrane. The membranes are 

 attached to the lower border of the first two or three caudal vertebrae, 

 thus permittmg them to be seen distinctly above, and to the upper bor- 

 ders of the remaining vertebnie, thus permitting them to be seen more 

 distinctly hclow. 



The skin of the two sides of the body unite in such wise as to per- 

 mit a very narrow interval to exist between the two layers. The upper 

 layer of the wing membrane is extending directly outward on a level 

 with the back of the chest and of the loin, but the lower layer is vari- 

 able It may extend outward as in the upper layer, but a disposition 

 exists for it first to conform to the curve of the side of the trunk and 

 join the upper layer near the union of the side with the upper surface 

 01 the trunk. In one remarkable instance, Chilonycteris davuL the 

 under layer extends quite to the middle line of the back, and thence is 

 deflected in an acute angle outward to join the upper layer. The re- 

 gion ot the axilla is greatly depressed in bats, owing to the inclination 

 tor the under skin layer to extend upward and backward. This space 

 IS so large as to suggest the adaptation of the pouch thus formed for 

 the protection of the young. In Gheiromeles it must have another sio-. 

 nificauce, since it here constitutes a huge bag-like involution whidi 

 extends as far as the middle line of the back. 



THE WING MEMBRANE AT REST. 



The bat when at rest folds the fingers by a movement of the root of 

 the hand (carpus) downward on the wrist end (distal end ) of the forearm 

 Ihis movement is characteristic and when completed brings the fino-ers 

 in a compact bundle (like the ribs of a closed umbrella) under the Ibre- 

 arm and parallel to it. The hand is thus tucked up toward the rest of 

 the anterior extremity, and as the forearm (in the same movement) is 

 sharply flexed on the arm the entire extremity presents the greatest 

 possible contrast to what it exhibited when prepared for flight The 

 bat now supports the body in one of two ways. It is prone, i. e., with 

 the front of the body downward on tlie plane of support, or it is pend- 

 ant, j. e., hung by the claws of the hind feet. If it is prone the base of 

 the thumb and wrist supports the body and is furnished with a hard- 

 ened pad of skin (callosity) for the purpose, tlie thumb being held at 

 the same time well out of the way, and the posterior extremity taking 



