METACARPUS. 225 



Peculiar Characters of the Metacarpal Bones. The metacarpal lone of the thumb 

 is shorter and wider than the rest, diverges to a greater degree from the carpus, 

 and its palmar surface is directed inwards towards the palm. The shaft is flat- 

 tened and broad on its dorsal aspect, and does not present the bifurcated ridge 

 which is found on the other metacarpal bones ; it is concave from before back- 

 wards on its palmar surface. The carpal extremity, or lose, presents a concavo- 

 convex surface, for articulation with the trapezium, and has no lateral facets. 

 The digital extremity is less convex than that of the other metacarpal bones, 

 broader from side to side than from before backwards, and terminates ante- 

 riorly in a small articular eminence on each side, over which play two sesa- 

 moid bones. 



The metacarpal bone of the index finger is the longest, and its base the largest 

 of the other four. Its carpal extremity is prolonged upwards and inwards. The 

 dorsal and palmar surfaces of this extremity are rough, for the attachment of 

 tendons and ligaments. It presents four articular facets : the first, at the end 

 of the bone, is concave from side to side, convex from before backwards, and 

 articulates with the trapezoid ; the second, on the radial side, is a flat quadri- 

 lateral facet, for the trapezium ; the third, which occupies the outer part of the 

 ulnar side of the extremity, is a long narrow facet, for the os magnum; and the 

 fourth, which occupies the inner part of the same side, is a considerably broader 

 surface, for third metacarpal bone. 



The metacarpal bone of the middle finger is a little smaller than the preceding; 

 it presents a pyramidal eminence on the radial side of its base (dorsal aspect), 

 which extends upwards behind the os magnum. The carpal articular facet is 

 concave behind, flat and horizontal in front, and corresponds to the os magnum. 

 On the radial side is a smooth concave facet, for articulation with the second 

 metacarpal bone ; and on the ulnar side two small oval facets, for articulation 

 with the fourth metacarpal. 



The melacarpal bone of the ring-finger is shorter and smaller than the preced- 

 ing, and its base small and quadrilateral ; the carpal surface of the base pre- 

 senting two facets, for articulation with the unciform and os magnum. On the 

 radial side are two oval facets, for articulation with the third metacarpal bone; 

 and on the ulnar side a single concave facet, for the fifth metacarpal. 



The metacarpal bone of the little finger may be distinguished by the concavo- 

 convex form of its carpal surface, which articulates with the unciform ; and 

 from having only one lateral articular facet, which corresponds with the fourth 

 metacarpal bone. On its ulnar side is a prominent tubercle, for the insertion 

 of the tendon of the Extensor carpi ulnaris. The dorsal surface of the shaft 

 is marked by an oblique ridge, which extends from near the ulnar side of the 

 upper extremity to the radial side of the lower. The outer division of this 

 surface serves for the attachment of the fourth Dorsal Interosseous muscle; the 

 inner division is smooth, and covered by the extensor tendons of the little finger. 



Articulations. The first metacarpal bone articulates with the trapezium; the 

 second with the trapezium, trapezoides, os magnum, and third metacarpal 

 bones ; the third with the os magnum, and second and fourth metacarpal bones ; 

 the fourth with the os magnum, unciform, and third and fifth rnetacarpal 

 bones ; and the fifth with the unciform and fourth metacarpal. 



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

 Flexor Ossis Metacarpi Pollicis, Extensor Ossis Metacarpi Pollicis, and first 

 Dorsal Interosseous. To the second metacarpal bone, five : the Flexor Carpi 

 Badialis, Extensor Carpi Badialis Longior, first and second Dorsal Interos- 

 seous, and first Palmar Interosseous. To the third, five : the Extensor Carpi 

 Eadialis Brevior, Flexor Brevis Pollicis, Adductor Pollicis, and second and 

 third Dorsal Interosseous. To the fourth, three : the third and fourth Dorsal 

 and second Palmar Interosseous. To the fifth, five: the Extensor Carpi Ulna- 

 ris, Flexor Ossis Metacarpi Minimi Digiti, fourth Dorsal, and third Palmar 

 Interosseous. 

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