BATS 



61 



and thus we find in the bat very powerful thoracic muscles, which 

 are attached to remarkably large shoulder-Hades and to a high bony 

 crest developed along the median line of the sternum, which thus 

 presents arrangements very similar to those which obtain in birds. 



2. How Flight is facilitated. The bones of the bat are not hollow 

 (pneumatic) like those of birds, nor do we meet with air-sacs within the 

 body cavity, as in the latter (which see), so that a diminution of the 

 weight of the body is brought about by other means. 



(a} All the bones (excepting the shoulder-blades and clavicles) are 

 extremely tliin, but at the same time rigid. 



(b) The supporting surface is much larger than in birds. In the latter 



THE LONG-EAKED BAT, WITH SKELETON MAKKED IN. (Natural size.) 



1, Thumb; 2, 3. 4. 5, remaining digits; C. (M.), carpal bones; Sp., spur; E.G. (Od.), ear- 

 covers. 



this surface is formed by the wings only and their feathers, whereas in 

 the bat it extends beyond the legs to the tail. 



(c) The size of the creature is small, the intestine short (see 

 Section B, 6 and 8). 



Nevertheless, progress through the air is a less easy task for the bat 

 than for the bird, with its specifically lighter body. Thus, the bat is not 

 able to soar in the air like a bird of prey (which see). To prevent itself 

 from falling, it must constantly keep its flying membrane in motion. As 

 in the case of other mammals, excessively strong movements of the fore- 

 limbs produce " loss or shortness of breath "; consequently the flight of 

 bats is not as enduring as that of birds (see the section on the Eespira- 

 tion of Birds). Bats can, however, move through the air with consider- 



