THORACIC LIMBS 



605 



Muscular Attachments. To the head of the pisiform is attached 

 the fiexor carpi ulnaris ; the distal surface of its shaft affords origin to 

 the abductor minimi digiti. 



Ossification. The pisiform develops from one centre of ossi- 

 fication. 



DISTAL ROW OF CARPAL BONES. 



FIG. 465. 

 Palmar Side. 



First Metacarpal. 

 Trapezium. 



Radial Side. 



Trapesoid. 



Magnum. 

 - Unciform. 

 With Cuneiform. 

 Fifth Metacarpal. 



FIG. 466. 



Dorsal Side. 



DISTAL ROW OF LEFT CARPAL BONES, PROXIMAL ASPECT. 



THE TRAPEZIUM. 



f 



General Description. The Trapezium is the smallest bone in 

 the carpus, except the small sesamoid articulating with the scapho- 

 lunar. It is the first bone on the radial side of 

 the distal row of the carpus (Figs. 465, 466), 

 where it lies behind and to the radial side of the 

 trapezoid, with its long axis running obliquely in 

 a dorso-ulnar direction. It is crescentic in shape 

 and presents five surfaces, proximal, dorsal, 

 palmar, radial, and ulnar. 



The proximal surface (Fig. 467) is nearly 

 square, or slightly narrowed at the dorsal end. 

 Its outer and inner margins are sharp and well 

 defined. Its posterior margin passes into the 

 rounded palmar surface. A faint ridge passing 

 in a dorso-radial direction divides the proximal 

 surface from the dorsal surface. The proximal 

 surface is almost flat, and is marked by a slight 

 groove which extends in a dorso-radial line at 

 right angles to the main axis of the bone. It 

 is covered with cartilage for articulation with 

 the facet on the under surface of the process of the scapho-lunar. 



POSITION OF TRAPEZIUM. 



