THE HAND. 195 



surface by which it articulates with the metacarpal bone of the 

 thumb, which he can do in a short time by a comparison of the 

 surfaces of the two bones. This being successful, will estab- 

 lish a clew to the other surfaces, and to the relative position of 

 the bone. The thumb surface is a concave cylindrical trochlea, 

 placed on the radial side of the trapezium, and looking down- 

 wards and outwards. On the reversed or upper side is a small 

 concavity, which receives the dorsal convexity of the scaphoid 

 bone. Continuous with this concavity is another on the ulnar 

 side, which receives a corresponding convexity of the trape- 

 zoides. Between this concavity and the one for the thumb is 

 a small plane surface, by which the trapezium articulates par- 

 tially with the metacarpal bone of the fore finger. The dorsal 

 face is rough and unequal. The palmar face is unequally di- 

 vided by a high ridge or process, at the ulnar side of whose 

 root is a deep fossa for the tendon of the flexor carpi radialis. 



Of the Trapezoides, (Trapezoide.) 



It is placed at the ulnar side of the last bone, and is the 

 smallest in the second row. There is no liability of confound- 

 ing it with any other bone of the carpus, as it is the least of 

 any, excepting the pisiforme. The greater difficulty is the ad- 

 justment of it in the separated bones: the following rule, how- 

 ever, will serve. It is surrounded by articular faces on its sides, 

 but the dorsal surface presents a broad base, while the palmar 

 extremity is reduced in siz.e. Holding the bone with a refe- 

 rence to these, it will be observed that one side is very crook- 

 ed and concave, while the reversed or opposite one is convex. 

 The latter fits against the surface of the trapezium which has 

 been indicated, while the former embraces the side of the os 

 magnum just below its head. The metacarpal surface of the 

 trapezoides is long and elevated in its middle for being received 

 into the root of the metacarpal bone of the fore finger, while 

 the upper surface presents a long concavity for receiving a part 

 of the dorsal convexity of the scaphoides. 



Of the Magnum, (Grand Os.) 



It is placed at the ulnar side of the trapezoides, and, from its 

 being larger than any other bone in the carpus, will scarcely 



