METACARPAL BONES 



93 



the unciform bone. Inferiorly this bone articulates by three distinct 

 surfaces, of which the middle is much the largest, with the second, 

 third, and fourth metacarpal bones. The os magnum articulates with 

 seven bones, viz., the scaphoid, semilunar, trapezoid, unciform, and 

 second, third, and fourth metacarpal bones. 



The unciform bone is readily distinguished by the large process 

 projecting forwards and curved slightly outwards pn its anterior sur- 

 foce. Seen from the front or behind, it has a triangular form. Its 

 external surface is vertical, and articulates with the os magnum ; its 

 inferior surface is divided into two facets which articulate with the 

 fourth and fifth metacarpal bones ; its superior surface, meeting the 

 cuneiform, is concavo-convex, incHnes upwards and outwards towards 

 the head of the os magnum, and is separated internally by a rough 

 border from the inferior surface. The unciform articulates with five 

 bones, viz., the os magnum, semilunar, cuneiform, and fourth and fifth 

 metacarpal bones. 



THE METACABPITS. 



The metacarpus, the part of the hand which supports the fingers, 

 consists of five shafted bones, diverging slightly from each other, and 

 which are numbered from without inwards. 



Fis. 79.- 



-The Eight Haxd from before. 

 (A. T.) 1 



Fix. 79. 



s, scaphoid bone ; I, semilunar ; c, cimeiform ; 

 p, pisiform ; t, trapezium ; next it the trape- 

 zoid, not lettered ; next the os magnum, also not 

 lettered ; u, unciform. 



I to V, the metacarpal bones ; 1, 3, first and 

 second phalanges of the thumb; 1, 2, 3, the 

 first, second, and third phalanges of the little 

 finger, and similarly for the other three fingers, 

 not marked ; * one of the sesamoid bones of the 

 thumb seen sideways. 



The metacarpal bones arc placed in 

 a segment of an arch transversely, and 

 being at the same time slightly curved, 

 longitudinally they present a concavity 

 directed forwards. They are terminated 

 at their carpal extremities by expanded 

 portions of different forms, and at the 

 digital ends by large rounded heads. 

 The first metacarpal bone is thicker 

 and shorter than the others. Of the remaining bones the third is the 

 longest and thickest, the second, fourth, and fifth decreasing regu- 

 larly in length, according to their position from without inwards. 



The sliafi of the first metacarpal bone is somewhat compressed from 

 before backwards, flat behind, and transversely convex in front. The 

 shafts of the others are prismatic, presenting a broad surface towards 

 the back of the hand, and towards the palm a rounded margin between 

 the two lateral surfaces. They are most slender immediately beyond 

 the carpal extremity, and become gradually thicker towards the head. 

 They present on their dorsal surfaces each a triangular subcutaneous 



