THE CARPUS. 201 
facets by two ridges—that: towards the radial side is for the base of the second 
metacarpal; the middle facet is for the third metacarpal; whilst the innermost 
facet of the three, not always 
present, very small and placed 
near the dorsal side of the bone, 
is for the fourth metacarpal. 
The outer side of the body has an 
articular surface for the trapezoid, 
not infrequently separated from 
the scaphoid surface on the head 
by a rough line, to which the 
interosseous ligament connecting 
it with the scaphoid is attached. 
The inner side of the body has an 
elongated articular surface, usually 
deeply notched in front, or it may 
be divided anteriorly into a small 
circular area near the dorsal edge ; 
and a larger posterior part. This 
latter articulates either singly or 
— doubly with the unciform, the in- 
- terosseous ligament which unites 
the two bones being attached Fic. 146.—THE RicHT TRAPEZOID. 
either to the notch or to the sur- 
face separating the two articular facets. The dorsal surface is rough for ligaments ; 
it is somewhat constricted below the head, the articular surface of which sweeps 
rounds its upper border. 
The os magnum articulates with seven bones—the uneiform, the semilunar, the 
scaphoid, the trapezoid, and 
the second, third, and fourth 
metacarpal bones ; occasion- 
Rae tvear pal ally the fourth metacarpal 
IT, Metacarpal 
Fer 
Trapezium 
Seaphoid 
Ill. Metacarpal 
IV. Metacarpal—_—*— 
. does not articulate with the 
3 Unciform magnum. 
a . Unciform Bone (os 
\ \ SSS \ TIT. Metacarpal hamatum).—The unciform 
IIT. Metacarpal : rye 
, can readily be distin- 
guished by the hook-like 
= process (hamulus) which pro- 
-£ jects from the lower and 
= inner aspect of its anterior 
surface. To this is attached 
the anterior annular liga- 
ment as well as some of the 
fibres of origin of the short 
muscles of the little finger. 
IV. Metacarpal 
~~Semilunar . . 
egal L&E \ The ulnar side of the unci- 
. 5 oN y "NePACAa 1 1 ‘ 
Semilunar las i to Sees pire form process 1s sometimes 
a grooved by the deep branch 
i 
of the ulnar nerve (Ander- 
son, W., “ Proc. Anat: Soc.” 
Journ. Anat. and Physiol. 
Vol. Msoxivillie pb lel ay) tqulhie 
Fic. 147.—THE Ricut Os Macnum. palmar surface, rough for 
ligaments, is somewhat. tri- 
angular in shape. Superiorly and internally there is an elongated articular surface 
for the cuneiform, convex above and coneave below. The owter aspect of the bone 
is provided with a plane elongated facet, occasionally divided into two (see above) 
for articulation with the os magnum. Where the superior and external surfaces 
i 4 
Unciform——?4 
i 
