THE CARPUS 



163 



the latter broad and rounded, constituting the widest surface of the bone, and both are rough 

 for the attachment of ligaments. The lateral surface slopes downward and medially and is 

 convex for articulation with the corresponding surface of the greater multangular. On the 

 medial surface in front is a smooth flat facet for the capitate; elsewhere it is rough for ligaments. 

 Articulations. — With the navicular above, second metacarpal below, greater multangular 

 laterallj', and the capitate medialty. 



The Capitate 



The capitate [os capitatum] or os magnum (fig. 196) is the largest bone of the 

 carpus. Situated in the centre of the \\Tist, the upper expanded portion, globular 

 in shape and known as the head, is received into the concavity formed above by 

 the navicular and lunate. The cubical portion below forms the body, whilst the 

 intermediate constricted part is distinguished as the neck. 



Fig. 196. 



For lunate 

 For navicular 



The radial or lateral side 



For lesser multangular 



For second metacarpal 



For third metacarpal 



-The Left Capitate. 



i"or lunate 

 For hamats 



The ulnar or medial side 

 For fourth metacarpal 



Of the sLx sm-faces, the superior is smooth and convex, elongated from before backward 

 for articulation with the concavity of the lunate bone. The inferior surface is divided into 

 three unequal parts by two ridges. The middle portion, much the larger, articulates with the 

 base of the third metacarpal; the lateral, narrow and concave, looks lateral as well as downward 

 to articulate with the second metacarpal, whilst the medial portion is a small facet, placed on the 

 projecting angle of the bone dorsally, for the fourth metacarpal bone. The volar surface is 

 convex and rough, giving origin to fibres of the oblique adductor pollicis; the dorsal surface is 

 broad and deeply concave. The lateral surface presents, from above downward; — ( 1) a smooth 

 convex sm-face, forming the outer aspect of the head, with the superior surface of which it is 

 continuous, for articulation with the navicular; (2) a groove representing the neck, indented 

 for ligaments; (3) a small facet, flat and smooth, for articulation with the lesser multangular. 

 Behind this facet is a rough area for attachment of an interosseous ligament. The medial 

 surface has extending along its whole hinder margin an oblong articular surface for the hamate; 

 the lower part of this smooth area sometimes forms a detached facet. The volar part of the 

 surface is rough for an interosseous ligament. 



Articulations. — With the lunate and navicular above, second, third, and fourth meta- 

 carpals below, lesser multangular laterally, and hamate medially. 



The Hamate 



The hamate [os hamatum] or unciform (fig. 197) is a large wedge-shaped bone, 

 bearing a hook-like process, situated between the capitate and triquetral, with 

 the base directed downward and resting on the two medial metacarpals. 



Fig. 197. — The Left Hamate. 

 Hamulus- 



Fifth metacarpal 

 Fourth metacarpal 



Capitate 



The apex of the wedge forms the narrow superior surface, directed upward and laterally 

 for articulation with the lunate. The inferior surface or base is divided by a ridge into two 

 quadrilateral facets for the fourth and fifth metacarpal bones. The volar surface is triangular 

 in outline and presents at its lower part a prominent hamulus (unciform process), a hook-like 

 eminence, projecting forward and curved toward the carpal canal. It is flattened from side 

 to side so as to present two surfaces, two borders, and a free extremity. To the latter the trans- 

 verse carpal ligament and the flexor carpi ulnaris (by means of the piso-hamate Ugament) are 

 attached, whilst the medial surface affords origin to the flexor brevis and the opponens digiti quinti. 

 The lateral surface is concave and in relation to the flexor tendons. The dorsal surface is 

 triangular and rough for ligaments. The lateral surface has extending along its upper and 



