228 



OSTEOLOGY 



For greater 

 multangular 



For greater 

 multangular 



FIG. 229. The first metacarpal. 

 (Left.) 



ward, on the volar than on the dorsal aspect, and is longer in the antero-posterior 

 than in the transverse diameter. On either side of the head is a tubercle for the 

 attachment of the collateral ligament of the metacarpophalangeal joint. The 

 dorsal surface, broad and flat, supports the Extensor tendons; the volar surface 

 is grooved in the middle line for the passage of the Flexor tendons, and marked 

 on either side by an articular eminence continuous with the terminal articular 

 surface. 



Characteristics of the Individual Metacarpal Bones. The First Metacarpal 

 Bone (os metacarpale I; metacarpal bone of the thumb) (Fig. 229) is shorter and 



stouter than the others, diverges to a greater degree 

 from the carpus, and its volar surface is directed 

 toward the palm. The body is flattened and broad 

 on its dorsal surface, and does not present the ridge 

 which is found on the other metacarpal bones; its 

 volar surface is concave from above downward. On 

 its radial border is inserted the Opponens pollicis; 

 its ulnar border gives origin to the lateral head of 

 the first Interosseus dorsalis. The base presents a 

 concavo-convex surface, for articulation with the 

 greater multangular; it has no facets on its sides, but 

 on its radial side is a tubercle for the insertion of the 

 Abductor pollicis longus. The head is less convex 

 than those of the other metacarpal bones, and is 

 broader from side to side than from before backward. 

 On its volar surface are two articular eminences, of 

 which the lateral is the larger, for the two sesamoid 

 bones in the tendons of the Flexor pollicis brevis. 

 The Second Metacarpal Bone (os metacarpale II; metacarpal bone of the index 

 finger) (Fig. 230) is the longest, and its base the largest, of the four remaining 

 bones. Its base is prolonged up\vard and medialward, forming a prominent ridge. 

 It presents four articular facets: three on the upper surface and one on the ulnar 

 side. Of the facets on the upper surface the intermediate is the largest and is 

 concave from side to side, convex from before backward for articulation with the 

 lesser multangular; the lateral is small, flat and oval for articulation with the greater 

 multangular; the medial, on the summit of the ridge, is long and narrow for articu- 

 lation with the capitate. The facet on the ulnar side articulates with the third 

 metacarpal. The Extensor carpi radialis longus is inserted on the dorsal surface 

 and the Flexor carpi radialis on the volar surface of the base. 



The Third Metacarpal Bone (os metacarpale III; metacarpal bone of the middle 

 finger) (Fig. 231) is a little smaller than the second. The dorsal aspect of its 

 base presents on its radial side a pyramidal eminence, the styloid process, which 

 extends upward behind the capitate; immediately distal to this is a rough surface 

 for the attachment of the Extensor carpi radialis brevis. The carpal articular 

 facet is concave behind, flat in front, and articulates with the capitate. On the 

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

 and on the ulnar side two small oval facets for the fourth metacarpal. 



The Fourth Metacarpal Bone (os metacarpale IV; metacarpal bone of the ring 

 finger) (Fig. 232) is shorter and smaller than the third. The base is small and 

 quadrilateral; its superior surface presents two facets, a large one medially for 

 articulation with the hamate, and a small one laterally for the capitate. On the 

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

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



The Fifth Metacarpal Bone (os metacarpale V; metacarpal bone of the little finger) 

 (Fig. 233) presents on its base one facet on its superior surface, w T hich is concavo- 



