Chap, x.] FLYING ORGANS OF MAMMALS. 385 



volar membranes. These, when best developed, con- 

 sist of (1) an " antebrachial membrane," which extends 

 from the shoulder to the base of the thumb ; (2) the 

 " wing membrane," which extends from the sides of 

 the body along the fore-arm and between the elongated 

 digits of the rnanus (3) an " interfemoral membrane," 

 which is attached to the hinder end of the body, and 

 to the sides of the leg as far as the heel, and in some 

 as far as the phalanges of the foot. The relation of 

 the antebrachial membrane to the power of flight is 

 spoken to not only by the extent of its development 

 in flying forms, but also by its reduction in such as 

 are best fitted for terrestrial progression. The most 

 important function of the interfemoral membrane 

 would appear to be that of acting as a rudder ; this 

 power is greatest when, as in the Molossi, the bat is 

 able to vary the extent of the membrane, for this 

 "must confer upon them great dexterity in quickly 

 changing the direction of their flight, as when obliged 

 to double in pursuing their swiftly-flying insect prey ' 

 (Dolson). 



Less well-marked powers of flight are possessed by 

 the aberrant insectivore Galeopithecus (the so-called 

 " flying lemur "), which has been observed to move 

 through seventy yards of air, and in which the two 

 pairs of limbs and the tail are connected together by 

 an expansion of the skin, which forms a parachute- 

 like enlargement ; this is not, however, merely mem- 

 branous, as in bats, but is hairy 011 either surface. 

 Among the Rodents the flying squirrel (Pteromys), 

 and among Marsupials the flying phalanger (Petau- 

 rus), have the fore and hind limbs connected by a fold 

 of skin, which, when the limbs are extended, forms a 

 similar kind of parachute, but it does not reach to the 

 tail, nor is their patagium provided, like that of Galeo- 

 pithecus, with any special muscles. 



Organs of flight are, among the Vertebrata, best 

 z 16 



