ClIIROPTKRA 



649 



and with the nasal and labial appendages have been described when 

 referring to the nervous system. It remains therefore to consider 

 its relative development as part of the organs of flight. 



The extent and shape of the flying-membranes depend mainly 

 on the form of the bones of the anterior extremities, and on the 

 presence or absence of the tail. Certain modifications of these 

 membranes, however, are met with which do not depend on the 

 skeleton, but are related to the habits of the animals, and to the 

 manner in which the wing is folded in repose. 



These membranes consist of the " antebrachial membrane,"' 

 extending from the point of the shoulder along the humerus and more 

 or less of the forearm to the base of the pollex, the metacarpal bone 

 of which is partially or wholly included in it; the "wing-membrane," 

 which is spread out between the greatly elongated fingers, and 

 extends along the sides of the body to the posterior extremities, 

 generally reaching to the feet ; and the " interfemoral membrane," 

 the most variable of all, which is supported between the extremity 

 of the body, the legs, and the calcar (Fig. 297). 



The antebrachial and wing-membranes are most developed in 

 those species fitted only for aerial locomotion, which when at 

 rest hang with the body enveloped in the wings ; but in the family 

 Emballonwridce, and especially in the subfamily Molossinm (the species 

 of which are the best fitted of all Bats for terrestrial progression), 

 the antebrachial membrane is reduced to the smallest size, and 

 is not developed along the forearm, leaving also the pollex quite 

 free, and the wing-membrane is very narrow and folded in repose 

 completely under the forearm. 

 The relative development of the 

 interfemoral membrane has been 

 referred to above in describing 

 the caudal vertebra?. Its small 

 size in the frugivorous and sangui- 

 vorous species, in which its presence 

 would be injurious as impeding 



their motions when searching for Fro. 300.-5*ontalsacand nose-leaf in inale 

 . , ,11 i i i an< i female of H ipposideruslarvatus. (Dobson, 



food as they hang suspended by Proc . Zo oi. Soc. 1873.) 

 their feet, is easily understood. 



Odoriferous glands and pouches opening on the surface of the outer 

 skin are developed in many species, but in most cases more so in 

 males than in females, and thus constitute secondary sexual char- 

 acters, which will be referred to when treating of the peculiarities 

 of certain species. 



All the fossil Chiroptera at present known are true Bats in every 

 sense of the word, and therefore throw no light on the origin of the 

 order. The earliest representatives of the order occur in beds 

 of Upper Eocene (Lower Oligocene) age. 



