METACARPUS. 87 



The number of articulations which each bone of the carpus presents 

 with surrounding bones, may be expressed in figures, which will 

 materially facilitate their recollection ; the number for the first row is 

 5531, and for the second 4475. 



METACARPUS. The bones of the metacarpus are five in number. 

 They are long bones, divisible into a head, shaft, and base. 



The head is rounded at the extremity, and flattened at each side, 

 for the insertion of strong ligaments ; the shaft is prismoid, and marked 

 deeply on each side, for the attachment of the interossei muscles ; and 

 the base is irregularly quadrilateral, and rough for the insertion of 

 tendons and ligaments. The base presents three articular surfaces, 

 one at each side, for the adjoining metacarpal bones ; and one at the 

 extremity for the carpus. 



The metacarpal bone of the thumb is one-third shorter than the 

 rest, flattened and broad on its dorsal aspect, and convex on its 

 palmar side ; the articular surface of the head is not so round as that 

 of the other metacarpal bones ; and the base has a single concavo- 

 convex surface, to articulate with the similar surface of the trapezium. 



The metacarpal bones of the different fingers may be distinguished 

 by certain obvious characters. The base of the metacarpal bone of 

 the index finger is the largest of the four, and presents four articular 

 surfaces. That of the middle finger may be distinguished by a 

 rounded projecting process upon the radial side of its base, and two 

 small circular facets upon its ulnar lateral surface. The base of the 

 metacarpal bone of the ring-finger is small and square, and has two 

 small circular facets to correspond with those of the middle meta- 

 carpal. The metacarpal bone of the little finger has only one lateral 

 articular surface. 



Development. By two centres ; one for the shaft, and one for the 

 digital extremity, with the exception of the metacarpal bone of the 

 thumb, the epiphysis of which, like that of the phalanges, occupies 

 the carpal end of the bone. Ossification of the metacarpal bones com- 

 mences in the embryo between the tenth and twelfth week, that is, soon 

 after the bones of the fore-arm. The epiphyses make their appear- 

 ance at the end of the second, or early in the third year, and the 

 bones are completed at twenty. 



Articulations. The first with the trapezium ; second, with the tra- 

 pezium, trapezoides, and os magnum, and with the middle metacarpal 

 bone ; third, or middle, with the os magnum, and adjoining metacarpal 

 bones ; fourth, with the os magnum and uncifonne, and with the ad- 

 joining metacarpal bones ; and, fifth, with the unciforme, and with the 

 metacarpal bone of the ring-finger. 



The figures resulting from the number of articulations which each 

 metacarpal bone possesses, taken from the radial to the ulnar side, 

 are 13121. 



Attachment of Muscles. To the metacarpal bone of the thumb, 

 three, the flexor ossis metacarpi, extensor ossis metacarpi, and first 



