^°l89yy^'] PROCEEDINGS OF THE NATIONAL MUSEUM 5 



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

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

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

 the position nearly the same as that of terrestrial quadrupeds. The 

 best example of those that scurry* when the wings are folded are the 

 JMolossi. In this group the phalanges of the third and fourth digits 

 are now no longer held in axial line with the metacarpals as in flight, 

 but are drawn upward and to the side, though well out of the way. 

 The tail in all prone forms remains extended and the tip touches 

 the plane on which the animal rests. If the bat is pendant in rest the 

 base of the thumb and wrist do not support. The thumb is without 

 callosity, is more engaged in the wing membrane, and is drawn more 

 or less in toward the under surface of the wing. In this event the foot 

 is furnished with sharper and more recurved claws, since they are now 

 prehensile. The leg assumes a position quite at variance with the ter. 

 restrial position and is different in this regard from all mammals, the 

 sloth alone excepted. The tail in the pendant form, at least in our red 

 bat, is drawn well forward and rests on the lower jjart of the trunk. It 

 is readily seen that very long digits of the anterior extremity would be 

 more or less in the way in the prone forms, while they might be extended 

 to any degree in the pendant forms, without interference. In fact the 

 first named have smaller digital elements than the last and the wing 

 expanse is correspondingly more restricted.t 



THE WING MEMBRANE IN FLIGHT. 



Wliile interesting characters are thus observed in the bat when at 

 rest it is in the use of the limbs in flight that the chief peculiarities are 

 noted. The intervals between the digits vary greatly in the different 

 genera. As already remarked the under surfaces of the second and 

 third digits are boldly outlined or are covered with membrane so as to 

 obscure their outlines. In the forms in which this obscuring is noticed 

 the fifth finger is supported by a little rod of cartilage. 



The opening of the wing exerts a ]^owerful influence over the posteKior 

 extremity. It pulls it outward in the forms in which an interfemoral 

 membrane is present and thus makes tense this membrane. The entire 

 limb is abducted from the terrestrial position and the foot is turned 

 with its i)lantar surface forward, 



*A Avoi-fl was needed to express the terrestrial motion of a bat whose wings are at 

 rest. I venture to use "scurry" in lien of a better. 



tThe contrast between prone and pendant positions of bats wlien at rest is an 

 instructive one. It supposes the existence of a number of adaptive characters, which 

 will l)e observed in the accounts of members of our fauna. So little is known of the 

 habits of bats that it would be premature to base any generalizations upon these or 

 any other isolated groups of structural peculiarities. I have seen our common brown 

 bat in captivity hang itself up by the claws, but have never seen it other than prone 

 when at rest in its native haunts. I am also aware that llhynchonycterxs (which has 

 a dexed thumb and a small potlical callosity) comes to rest like a moth; i. e., with 

 wings expanded yet prone. 



