82 



THE BIOLOGY OF BIRDS 



vibration of the wings, far more rapid in most cases than 

 anything seen among birds. Thus a bee vibrates its wings 

 more than 200 times in a second, and for a short distance 

 the bee can outfly the pigeon. 



In Pterodactyls an extension of the skin was borne out 

 on the extremely elongated outermost finger, usually 

 counted as the little finger. The power of flight was 

 probably not very great, for the keel on the breastbone, to 

 which the muscles working the wings would be attached, is 

 at most slight. 



In bats a double fold of skin, beginning at the sides of 



TH 



H 



Fig. 20. — Bat's wing and skeleton. From a specimen. H., humerus ; 

 u., splint-like ulna; r., radius; w., wrist; th., thumb; mc.2, second 

 metacarpal or palm bone ; mc.s, fifth metacarpal ; ph.i and ph. 2, its two 

 phalanges or finger-joints; E., elbow; Ti., tibia; Fi., splint-like fibula ; 

 F., femur; i.f.m., inter-femoral membrane ; c.v., caudal vertebra; ; c.v., 

 just below the skull refers to cervical vertebra; ; CL., clavicle ; sc, scapula ; 

 ST., sternum ; R., ribs ; L.v,, lumbar vertebra3 or loins ; IL., ilium ; P., 

 pubis ; IS., ischium, 



the neck, is stretched out along the anterior margin of the 

 arm, and, skipping the thumb, is continued between the 

 greatly elongated metacarpals and phalanges to form the 

 wing proper. This tapers off, however, down the side of 

 the body to the hind leg, and between the hind legs to each 

 side of the tail (forming the inter-femoral membrane) if 

 there is a tail. 



