144 ZOOLOGY. 



it and the carpal bones a fibre-cartilage of a triangular shape, 

 which attaching the radius at its extremity to the ulna, 

 permits the former to rotate around the lower end of the 

 latter, which remains fixed. 



These two bones at their carpal extremities also move 

 readily in flexion and extension. 



The process called olecranon belongs to the ulna or cubit ; 

 to it are attached the extensor muscles of the fore-arm. 



276. In the hand we have the carpus, metacarpus, and 

 fingers, or digital portion. 



The carpus is composed of eight bones, four in each row j 

 they are scarcely moveable, and the strength of the arch they 

 form is considerable. In the first row we find the scaphoid, 

 semilunar, pyramidal, and pisiform; in the second row the 

 trapezium, trapezoides, magnum, and unciform. On the 

 flexor side of the hand they form with the anterior annular 

 ligament of the carpus, a canal, in which are lodged and 

 protected most of the flexor tendons, and one of the great 

 nerves (median) proceeding to the palm of the hand. 



The metacarpus is composed of a single row of small long 

 bones, corresponding to the number of the fingers, all diffe- 

 rent and readily distinguishable from each other. Four of 

 these move but little ; the first, which supports the thumb, 

 and which some view as the proximal phalanx of that finger, 

 is very moveable, corresponding to the greater mobility of 

 the thumb as compared with the other fingers. 



Finally, the fingers have each three bones, called proximal, 

 middle, and distal phalanges ; in the thumb there are only 

 two. The distal phalanx supports the nail, and is sometimes 

 called the nail-bone, or ungual phalanx. 



277. When we consider the arm as a series of broken 

 levers, we observe that the arm is longer than the fore-arm, 

 and this longer than the hand : or, in other words, that the 

 mobility of the structures and their flexibility and power of 

 adaptation increase as we approach the extremity, properly so 

 called. 



278. The structure of the inferior or pelvic extremities 

 has the strongest analogy to that of the superior limbs, and 

 the principal differences to be observed have a necessary 

 relation to their functions ; to make of them, in fact, instru- 

 ments of locomotion rather than of prehension. Hence their 

 solidity, at the expense of their mobility. They also have a 

 basilar portion, the haunch, the representative of the shoulder, 



