3H 



HUMAN ANATOMY. 



magnum are the first to ossify, the process beginning in the latter part of the first 

 year. The order of its appearance in the other bones is very uncertain. Those of 

 the first row, excepting the pisiform, contain bone by the end of the first five or six 



Fig. 337. 



c 



Ossification of bones of hand. A, at birth; B, latter half of first year ; Cat three years; D, at eitht years; 

 £, at twelve years, a, centres for shafts of metacarpals and phalanges ; d, magnum ; c, unciform ; d. cuneiform , 

 e, base of first metacarpal ; y, heads of metacarpals; g-, bases of proximal phalanges; /z, .bases of distal phalanges; 

 J, scaphoid ; /, trapezium ; k, trapezoid ; /, semilunar ; m, bases of middle phalanges ; n, pisiform. 



years. These are followed by the trapezium and the trapezoid, so that by the eighth 

 year the process has begun in all the carpals save the pisiform, in which it begins 

 about the twelfth year. 



THE METACARPAL BONES. 



The metacarpal bone of the thumb ' in many respects resembles a phalanx and 

 calls for a separate description; the others have the following points in common. 

 They possess a shafts and two extremities, of which the proximal is the dase and the 

 distal the head} Each base^ has an articular surface at the end to join the carpus and 

 one on the side or sides that come into contact with the other metacarpal bones, with 

 a depression for an interosseous ligament beyond it. The bases themselves are 

 cubical and rough both above and below. The shaft narrows in front of the base, 

 and has a median dorsal ridge^ which soon divides into two lines running to either 

 Side of the head, thus bounding a long, flat dorsal surface occupying more than half 

 the bone. A palmar ridge runs nearly the whole length of the shaft, dividing very 

 near the head into two faint lines to either side of it. Thus, near the base the 

 shaft may be called cylindrical, with a ridge above and below, while farther forward 

 it has a dorsal and two lateral sides. This description applies most closely to the 

 bone of the index, and becomes less and less accurate as we proceed to the little 



' 0* metacarpale I. "Corpus. ^Capitulum. ''Basis. 



