I BULLETIN 43, UNITED STATES NATIONAL MUSEUM, 



above is less constant in form and dimensions. It may be gnided by a 

 long tail quite to its tip, it may allow the tip to project in different de- 

 grees beyond its free margin, it may greatly exceed in size that of the 

 stunted tail, it may be defined as a hem along the inner border of the 

 limbs, or it may be entirely absent. 



It follows from these statements that all bats are provided with a 

 back and a front skin-expanse from the sides of the body to the extremi- 

 ities in a constant manner, bat from the tail to the posterior extremities 

 in an inconstant manner, the last named presenting modifications deter- 

 mined by degrees of outgrowtli of the tail itself. 



The membranes present many details with respect to the manner of 

 their attachment to the sides of the body and to the various parts of 

 the limbs. Interesting variations of plan are seen where the skin 

 crosses joints. In the elbow joint the skin may be attached entirely to 

 the epicondyle, so that the joint lies quite to the under side of the 

 wing, as in the African fox-bat, Upomojjhorus; or it may be attached 

 midway, namely, to the olecranon, as in many forms, but perhaps best 

 seen in the neotropical American SaccojHerj/x; or it may be attached 

 entirely to the epitrochlea, so that the joint lies quite on the upper sur- 

 face of the wing, as in Ehinolophus pearsoni and Taphozous. At the 

 wrist distinctions are seen in the manner in which the tendons of the 

 extensor carpi ulnaris and flexor carpi ulnaris are dis])osed at the angle 

 which is formed between the radius and the fifth metacarpal bone. 

 When this angle is marked, and skin-folds are conspicuous over the 

 tendons named, a radio-metacarpal pouch is defined. The knee always 

 lies on the upper surface of the membrane. It is most free in Mucrotus 

 and least so in the Molossi.* The membrane attached to the ankle may 

 lie entirely to the hallucal side of the joint, but is disposed to cross it 

 by an oblique raised fold and be secured to the minimal, /. e., little toe 

 side. 



I have found it convenient to employ a number of names for the sub- 

 divisions of the dermal expanse. 



The membrane which extends from the sides of the trunk to include 

 the anterior extremity is the wing membrane ("bat wing," patagium). 



The membrane between the legs is the interfemoral membrane (uro- 

 patagium). 



The wing membrane above the arm and forearm is the prebrachium 

 (antebrachial membrane, propatagium). 



The wing membrane below the arm and forearm would become anti- 

 thetically the postbrachiuni. But since the postbrachium could not be 

 separated from the sides of the trunk and the legs, it has been found 

 necessary to discard it. 



The part of the Aving membrane lying between the body, the humerus, 



*The group named the Molossi Avill be held in this essay to be distinct from the 

 group of which Emballonura is the central genus. I am of the opinion that these 

 alliances are distinct and coequal. 



