SKELETON OP THE BAT. 



775 



necessary weight is here permitted. It is, however, in the construction 

 of the anterior limbs that the Cheiroptera present the most remarkable 

 peculiarities. The scapulae are broad and expanded, covering a con- 

 siderable portion of the back of the thorax, thus giving a firm basis to 

 the wing. The clavicles are large and perfectly formed, in order to 

 resist the powerful action of the pectoral muscles used in depressing the 



Fig. 394. 



Skeleton of the Bat. 



wings during flight; and in order to give those muscles a sufficient 

 extent of origin, the sternum, although exhibiting the general charac- 

 ters of that of a quadruped, is deeply carinated along the mesial line. 

 The humerus is of moderate length, but the fore-arm prolonged and 

 slender ; it consists, in fact, of but one bone, so that all movements of 

 pronation and supination are necessarily impracticable. The carpal 

 bones present their usual structure and arrangement at the base of the 

 hand ; but those of the metacarpus, excepting that of the thumb, are 

 so extraordinarily lengthened, that they themselves form a considerable 

 portion of the framework of the wing, which is completed by the pha- 

 langes of the fingers appended to their extremities. All these wire- 

 like fingers are connected together by a broad duplicature of skin, 

 derived from the sides of the body, which is continued along the whole 

 length of the hind legs, and even fills up the interspace between these 

 last and the tail : this membrane forms an expansion sufficiently ex- 

 tensive to become converted into an organ of flight. The fingers com- 

 posing this strange hand are obviously incapable of closing towards the 

 palm, as ours do when grasping an object : their only movements are 

 such as fold up the wing against the side of the body, by laying the 

 fingers close along the side of the fore-arm, as in closing a fan. The 

 thumb alone is left free ; and this being short, and armed with a strong 

 nail, is employed in enabling the creature to cling to some elevated 

 object in those gloomy lurking-places wherein it hides during the day. 

 (2230.) The QUADBUMANA, next to mankind the most elevated mem- 



