BONES AND MUSCLES OF ARM AND HAND. 481 



be otherwise inapplicable. It is only among the higher 

 orders of Quadrupeds, however, that it can possibly be exe- 

 cuted ; for in the lower, the two bones are united more or less 

 completely into one, or are articulated in such a manner as to 

 be incapable of rotation. 



640. The fore-arm is bent upon the arm, chiefly by muscles 

 that lie upon the front of the latter ; of these the principal is 

 the biceps or two-headed muscle ( 7 , fig. 227), which arises from 

 the coracoid process of the scapula, and from the top of the 

 glenoid cavity, and is inserted into the radius a little in front 

 of the elbow, forming a great part of the fleshy mass in front 

 of the arm (fig. 2 1 9). The arm is straightened again by a large 

 muscle, the triceps or three-headed muscle, which arises from 

 the back of the humerus and scapula, and passes down to be 

 inserted into a projection of the ulna behind the elbow-joint, 

 forming the fleshy mass at the back of the arm. The muscles 

 which rotate the fore-arm arise from the lower end of the 

 humerus, or from one of its own bones, and pass obliquely 

 across to the other. 



641. The Hand is anatomically divided into three portions, 

 the carpus^ metacarpus, and phalanges (fig. 223). The 

 carpus, which is the portion nearest the wrist-joint, is com- 

 posed of eight small short bones, which are firmly united to 

 each other by ligaments, but yet have a certain degree of 

 motion permitted them ; these are arranged in two rows, of 

 which one has a rounded surface, and enters into the forma- 

 tion of the wrist-joint ; whilst the other has a series of shal- 

 low pits, to receive the rounded heads of the metacarpal 

 bones. These last almost precisely resemble the bones of the 

 fingers, and in the skeleton might be mistaken for their first 

 joints ; but with the exception of that of the thumb they are 

 all united to each other by ligaments and muscles, so as to 

 form the compact framework which gives support to the palm 

 of the hand. The metacarpal bone of the thumb is much 

 more free in its movements ; and it is chiefly by an alteration 

 in its direction, that the thumb can be opposed to the fingers. 

 The thumb and fingers are formed by a series of small bones 

 which are termed the phalanges; of these there are only two 

 in the thumb, whilst there are three in the fingers. They are 

 bent on each other chiefly by the action of the muscles that 

 occupy the front of the fore-arm ; and they are extended or 



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