48(j THE MECHANICAL FUNCTIONS. 



heights ; but these appendages to the body are mere 

 parachutes, not wings ; and none of the animals 

 which possess them can, by their means, and with 

 the utmost eftbrts which their muscles are capable 

 of exerting, ever rise from the ground, or even sus- 

 pend themselves for a moment in the air. 



The only quadruped that can properly be said to 

 be endowed with the power of flying is the Bat. 

 In this animal the portions of the skeleton (f, Fig. 

 223) which correspond to the phalanges of the 

 fingers, are extended to an enormous length ; and 

 the pectoral muscles, which move the anterior ex- 

 tremities, are of extraordinary size and power. In 

 the larger species, each wing is at least two feet in 

 length. The fine membrane, which is spread be- 

 tween these lengthened fingers, has its origin in the 

 sides of the neck, and reaches all along the body 

 to the extremities of the hinder legs, which it en- 

 closes in its folds. Thus, not only is the surface, 

 by which it acts upon the air, sufficiently extensive, 

 but the muscular power, by which its motions are 

 effected, is adequate to give it those quick and 

 sudden impulses which are requisite for flying ; 

 and thus, although its structure is totally different 

 from that of birds, it yet performs fully the office of 

 a real wing. The bat flies with perfect ease, even 

 while carrying along with it one or two of its 

 young : it is not, however, fitted for very long 

 flights. 



The conformation of the skeleton is adapted to 

 this new and important function. The chest is 

 broad and capacious, to admit of free respiration 

 while the animal is flying, and to afibrd ample 

 space for the attachment of the large muscles 



