47*2 THE MECHANICAL FUNCTIONS. 



placed on the inside of the ribs and sternum, 

 that is, between the carapace and plastron.* 

 The humerus is remarkably curved, especially 

 in the tortoise, where it has the form nearly of 

 a semi-circle. The radius and ulna are dis- 

 tinct from each other ; the carpus and phalanges 

 are short and stunted, forming a compressed 

 kind of hand. 



The pelvis, like the scapula and clavicle, is 

 enclosed within the bony shell which protects 

 the trunk. The sacrum is moveable upon the 

 last dorsal vertebra ; and the coccygeal vertebrae 

 are continued from it, forming a short tail. The 

 femur is short and powerful, and somewhat bent, 

 but less so than the humerus ; and the rest of 

 the bones of the hind extremity are similar to 

 those of the fore leg.f All the feet are joined 

 obliquely to the limbs which support them, 

 giving the animal an apparent awkwardness 

 of gait, as if it were obliged to walk upon club 



* The anomalous situation of these bones, and the strangely 

 disguised forms which their several parts assume, render it very 

 difficult to recognise in the skeleton the several pieces which 

 correspond to the normal type of the scapula, acromion, cora- 

 coid bone, and clavicle ; and anatomists are not yet agreed as 

 to the proper designations which are applicable to these bones 

 in the Chelonia. 



t The cylindrical bones of the tortoise are solid throughout, 

 and have no cavity for containing marrow, as in the more highly 

 developed bones of the mammalia. This is seen in the section 

 of the femur, Fig. 214. . . 



I 



