ORGANS OF LOCOMOTION. 



83 



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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 

 or less numerous in different classes, 

 and which is divided into three parts, 

 namely, the carpus, or wrist, (e,) the 

 metacarpus, or palm, (jf,) and the pha- 

 langes, or fingers, (g.) The clavicle or 

 collar-bone, (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 c- 

 shoulders separated ; to this end, we 

 find it fully developed in all animals 

 which raise the limbs from the sides, as 

 the birds and the bats. On the other 

 hand, it is rudimentary, or entirely want- 

 ing in animals which move them back- 

 wards and forwards only, as with most 

 quadrupeds. 



173. The following outlines, in which corresponding bones 

 are indicated by the same letters, 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 cylindrical, and en- 

 larged at its extremities ; the bones of the fore-arm are 

 somewhat shorter than the humerus, but more slender ; the 

 hand is composed of the following pieces, namely, eight 

 small bones of the carpus, arranged in two rows, five meta- 

 carpal bones, which are elongated, and succeed those of the 

 wrist ; five fingers of unequal length, one of which, the 

 thumb, is opposed to the four others. 



Fig. 34. 



