76 OSTEOLOGY. 



above, the magnum externally, the large and inner metacarpals 

 below, and the pisiform postero-internally. 



OS MAGNUM. 



(Fio. 16. 6.) 



The os magnum, the largest bone in the carpus, and the 

 central one in the lower row, is somewhat triangular in shape, 

 and presents four surfaces, a base, and an apex. The superior 

 surface is divided into two portions by a ridge, the concave inner 

 part articulating with the scaphoid, and the external, which is 

 oblong and concavo-convex, with the lunar bone. The inferior 

 surface, smooth and flat, rests on, and articulates with, the large 

 metacarpal bone, having also a very small bevelled portion near 

 its inner surface, which articulates with the inner metacarpal 

 bone. The internal surface is rough and irregular, and has 

 three facets which articulate with the trapezoid ; the external 

 surface joins the unciform, having two -facets. The base is 

 placed anteriorly, it and the apex both being roughened for 

 ligamentous attachments. 



The os magnum articulates with six bones viz., the scaphoid 

 and lunar above, the large and inner small metacarpals below, the 

 trapezoid internally, and the unciform externally. 



UNCIFORM BONE. 



(Fio. 16. 5.) 



This, the external bone of the lower row, is very irregular in 

 form, and somewhat resembles the trapezoid ; it has four surfaces, 

 a base, and an apex. The superior surface, convex from side 

 to side, and sloping externally, articulates with the lunar and 

 cuneiform bones. The inferior surface articulates by two facets 

 with the large, and one with the small metacarpal bone. The 

 internal surface presents two facets, which articulate with the 

 os magnum. The external surface is narrow ; the base is 

 situated anteriorly, the apex being the prominent unciform pro- 

 cess, and all the three parts are roughened for ligamentous 

 attachment. 



The unciform articulates with five bones viz., the lunar and 

 cuneiform above, the magnum internally, and the large and 

 external metacarpals below. 



