552 THE MECHANICAL FUNCTIONS. 



and sudden impulses which are requisite for 

 flying : and thus, although its structure is to- 

 tally 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 afford ample 

 space for the attachment of the large muscles 

 which have become necessary. The scapulae 

 (s) are large, and of a singular form, and they 

 are kept at a considerable distance asunder by 

 the expanded chest : their coracoid processes 

 are also large, and extend in the direction of the 

 sternum. The clavicles (c) are of enormous size 

 and length, being larger than either the scapula 

 or the sternum, and remarkably curved in their 

 shape. The sternum is much developed, ex- 

 tending laterally, and having a projecting crest 

 along the middle of its lower surface. The hu- 

 merus (h) is strong, but short ; apparently in 

 order to avoid the danger of its being snapped 

 asunder by the violent actions of the pectoral 

 muscles, had it been longer. As the leading 

 object of the structure is to give power to the 

 wing, there was no necessity for the rotatory 

 motion of the bones of the fore-arm ; and ac- 



