198 THE METACARPUS. 



ficial cavity, slanting inwards ; the external posterior angle of 

 which is so prominent, as to have the appearance of a process. 

 The external side of this base is made plane in the same way 

 as the external side of the former bone, while its internal side 

 has two hollow circular surfaces, for joining the third metacarpal 

 bone ; and between these surfaces there is a rough fossa, for the 

 adhesion of a ligament, and lodging mucilaginous glands. The 

 extensor carpi radialis brevior is inserted into the back part of 

 this base. The two sides of this bone are almost equally flat- 

 tened ; but the ridge on the forepart of the body inclines inwards. 

 The tubercles at the forepart of the root of the head are equal. 

 The motion of this bone is very little more than that of the 

 former ; and therefore these two firmly resist bodies pressed 

 against them by the thumb or fingers, or both. 



The metacarpal hone of the ring finger is shorter than the 

 second metacarpal bone. Its base is semicircular and convex, 

 for its conjunction with the os unciforme. On its external side 

 are two smooth convexities, and a middle fossa, adapted to the 

 second metacarpal bone. The internal side has a triangular 

 smooth concave surface to join it with the fourth one. The 

 anterior ridge of its body is situated more to the inside than to 

 the outside. The tubercles near the head are equal. The mo- 

 tion of this third metacarpal bone is greater than the motion of 

 the second. 



The metacarpal hone of the little finger is the smallest and 

 sharpest. Its base is irregularly convex, and rises slanting 

 inwards. Its external side is exactly adapted to the third meta- 

 carpal bone. The internal has no smooth surface, because it is 

 not contiguous to any other bone ; but it is prominent where 

 the extensor carpi ulnaris is inserted. As this metacarpal bone 

 is furnished with a proper moving muscle, has the plainest articu- 

 lation, is most loosely connected and least confined, it not only 

 enjoys a much larger motion than any of the rest, but draws 

 the third bone with it, when the palm of the hand is to be made 

 hollow by its advancement forwards, and by the prominence of 

 the thumb opposite to it. 



