ORGANS OF LOCOMOTION. 



59 



f 



a. 



\ I 



\ 



Cd 



Hade or scapula (a), a broad and flat bone, applied upon 

 the bones of the trunk ; 2. The arm (Z>), formed of a single 

 long cylindrical bone, the humerus ; 3. The fore arm, com- 

 posed of two long bones, the radius (c), and ulna (d), 

 which are often fused into one ; 4. The hand, which is 

 composed of a series of bones, more f .o 



or less numerous in different classes, 

 and which is divided into three parts, 

 namely, the carpus or wrist (e), the 

 metacarpus or palm (f), and the 

 fingers (g). The clavicle or collar- 

 lone (o), when it exists, belongs also 

 to the anterior member. It is a 

 bone of a cylindrical form, fixed as 

 a brace between the breast-bone and 

 shoulder-blade. Its use is to keep the 

 shoulders separated ; to this end, we 

 find it fully developed in all ani- 

 mals which raise the limbs from the 

 sides, as the birds and the bats. 

 On the other hand, it is rudimentary, 

 or entirely wanting in animals which 

 move them backwards and forwards 

 only, as with most quadrupeds. 



173. The following outlines will give an idea of the 

 modifications which these bones present, in different 

 classes. In the arm of man, (Fig. 34), the shoulder 

 blade is flat and triangular ; the bone of the arm is cylindri- 

 cal, and enlarged at its extremities ; the bones of the fore 

 arm are about the same length as the humerus, but more 

 slender ; the hand is composed of the following pieces, 

 namely, eight small bones of the carpus, arranged in two 

 ranks, five metacarpal bones, which are elongated, and 



Fig. 34. 



