THE METACARPUS 133 



The Unciform 



The unciform is the most readily recognised of all the carpals, as its palmar 

 surface presents a prominent hook-like process; this, the unciform process, has 

 its concavity directed towards the radial side, and forms part of the inner l)oundary 

 of the passage for the flexor tendons; to the apex of the process the anterior annular 

 ligament gains an attachment. It also affords origin to i\\e flexor brevis minimi and 

 opponens minimi digiti muscles. The dorsal surface is rough for ligaments. The 



Fig. 143. — The Left Unciform. 



unciform process- 



FIFTH METACARPAL 

 FOURTH METACARPAL 



inferior surface has two facets for the bases of fourth and fifth metacarpals. The 

 superior surface forms the apex of a wedge, and is smooth and rounded for articu- 

 lating with a narrow facet on the ulnar side of the lower surface of the semilunar. 

 The ulnar surface is mainly articular for the cuneiform, whilst the radial surface 

 is faceted for the magnum. 



Articulations. — With the cuneiform, semilunar, magnum, and the fourth and 

 fifth metacarpals. 



The central is an occasional element of the carpus. It is situated on the 

 dorsal aspect of the carpus, between the scaphoid, magnum, and trapezoid. This 

 bone is a normal element of the carpus in many mammals, even in the orang and 

 gibbon. It is represented in the carpus of the human embryo, but in most indi- 

 viduals it undergoes suppression or coalesces with the scaphoid. 



Blood-supply. — The arterial twigs to the carpal bones are derived from the 

 anterior and ])Osterior carpal branches of the radial and ulnar arteries. A large 

 l)ranch from the anterior interosseous is also distributed to the carpus, and twigs are 

 furnished to it from the posterior interosseous artery. 



Ossification. — At birth the carpal elements are cartilaginous, and the nucleus 

 for each bone appears in the following order: — 



Magnum, first year. 

 Unciform, second year. 

 Cuneiform, third year. 

 Semilunar, fourth year. 



Trapezium, fifth year. 

 Scaphoid, sixth year. 

 Trapezoid, eighth year. 

 Pisiform, twelfth year. 



THE METACARPUS 



The metacarpus consists of five bones. Each metacarpal Ijone has a shaft, a 

 rounded distal end termed the head, and a square-shaped proximal extremity 

 named the base. The shaft is prismatic; two surfaces of the prism are lateral, and 

 the third dorsal. The lateral surfaces afford attachment to the interosseous muscles: 

 on the palmar aspect of the shaft these surfaces approach each other, and for some 

 distance are only separated by a prominent ridge. The dorsal surface is smooth 

 and covered in the recent state by the tendons of the extensor muscles of the 

 fingers. Near the base, this surface is divided by a median ridge; as this ridge 

 passes to the distal end of the shaft, it divides and forms two ridges which termi- 

 nate in a prominent tubercle on each side of the head of the bone. The smooth 

 surface on each side of the median ridge on the dorsal aspect, near the base, is for 

 a dorsal interosseous muscle. The base is cpiadrilateral ; its palmar and dorsal sur- 

 faces are rough for ligaments; the ui)})er end articulates with the carpus, and its 

 lateral aspects have facets for adjacent metacarpals. The head has a semilunar 



