656 



MAMMALIA. 



extremities, whereby they are converted into most efficient instru- 

 ments for digging beneath the soil. The extended scapula, the 

 strong and well-developed clavicle, the square and massive hume- 

 rus, and, moreover, the broad and rake-like hand, all proclaim 

 the office of this strange limb ; while the long and carinated ster- 

 num indicates with equal plainness the size and power of those 

 muscles by which the apparatus is wielded.* 



(737.) The CHEIROPTERA, or family of BATS, present a 

 striking contrast to the Mole both in form and habits : neither 

 would it be easy to conceive that a skeleton, consisting almost of 

 precisely the same elements, could be converted to uses so diame- 

 trically opposite. 



Fig. 308. 



In these Mammalia the anterior extremities are converted into 

 wings, enabling them to emulate the very birds in their powers 

 of flight, and in the velocity of their movements, when upon the 

 wing pursuing insect prey. In creatures destined to such a life, 

 the whole skeleton must of course be lightened, and the bones 

 attenuated to the utmost. The skull, the spine, the thorax, 

 the pelvis, and the hind extremities, all testify by the delicacy 

 of their structure that no unnecessary 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 considerable 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 



* For an admirable history of the habits of the Mole, the reader is referred to Bell's 

 British Quadrupeds, page 85. 



