312 



HUMAN ANATOMY. 



distally and towards the palm there is a rough surface for hgaments. The styloid 

 process of the third metacarpal olten reaches the dorsal aspect of the trapezoid 



Fig. 331. 



Dorsal surface 



Fig. 



00^ 



For second 

 metacarpal 



For second 

 metacarpal 



For trapezium 



For magnum 

 Right trapezoid, inner aspect. 



Right trapezoid, outer and distal aspect. 



between the os magnum and the second metacarpal. The trapezoid articulates with 

 four bones, — the scaphoid, trapezium, os magnum, and second metacarpal. 



The OS magnum [os capitatum] is the largest bone of the carpus, and possesses 

 a head, neck, and body. The head is a rounded articular eminence at the proximal 

 end, playing in a socket formed by the scaphoid, semilunar, and unciform. The con- 

 vex articular surface extends much farther on the dorsal side than on the palmar. A 

 faint line above often separates the part resting on the scaphoid from that resting on 

 the semilunar. The former extends down the outer side of the head. The inner 

 side of the head is a sharply cut plane surface articulating with the unciform. The 

 neck is a constriction, best marked on the dorsal aspect, generally seen on all sides 

 except the inner. The distal surface, broader on the dorsal end, faces a little out- 

 ward. It is wholly articular, bearing the third metatarsal bone. A groove in the 

 place of the outer angle receives the edge of the second metatarsal. A smaller 

 surface for the fourth exists at the inner angle just below the dorsum. The dorsal 



Head 



Fig. 333. 



For unciform 



For 

 semilunar 



For fourth 

 metacarpal 



Neck 

 Right OS magnum, inner aspect. 



Fig. 334. 



Dorsal surface Neck For scaphoid 



For third 

 metacarpal 



For second 

 metacarpal 



For trapezoid 



Head 



For semilunar 



Right OS magnum, outer aspect. 



surface shows the head, and distally to it a sharp, slightly concave inner border, a 

 shorter outer one, and a distal one slanting downward and inward, so that the outer 

 angle is obtuse and the inner would be acute, but that the point of the angle is 

 replaced by a small border touching the fourth metacarpal. The palmar surface is 

 narrow and prominent below the neck. The inner surface is rough for a ligament 

 near the palmar border ; above, it has a narrow articular surface for the unciform, 

 continuous with that on the head. The 07iter surface has a small articulation with 

 the trapezoid, which exceptionally is continuous with the facet on the head. The 

 os magnum articulates with scj'cn boneS, — the scaphoid, semilunar, trapezoid, unci- 

 form, and second, third, and fourth metacarpals. 



The unciform [os hamatum] is distinguished by a prominent hook projecting 

 from the inner side of the palmar surface for a part of the annular ligament. The 

 dorsal surface is nearly or quite triangular. It presents an oblique proximal border, 

 a nearly straight, but often convex, outer one, and a distal one tending to meet the 

 inner end of the proximal border. Should they meet, the surface is triangular ; but 

 more often there is a very short inner border separating them, which is either straight 



