200 OSTEOLOGY. 
facet on its inferior surface for articulation with the metacarpal bone of the thumb. 
From its palmar aspect there rises a prominent ridge, within which is a groove along 
which the tendon of the flexor carpi 
os ae Lig Paantienan radialis muscle passes. The ridge 
}neiform—~ , € : ; z = 
“3 yo furnishes an attachment for the an- 
terior annular ligament, as well as for 
some of the short muscles of the thumb. 
The superior surface has a half oval 
facet for the scaphoid, external to which 
it is rough, and becomes continuous 
with the non-articular external aspect, 
which serves for the attachment of 
ligaments. On its inner surface there 
are two facets; the upper is a half 
oval, concave from above downwards, 
and very shghtly convex from before 
backwards, and is for articulation with 
the trapezoid. The lower, small and 
circular, and not always present, is for 
articulation with the outer side of the 
base of the second metacarpal bone. 
The dorsal surface, of irregular outline, 
is rough for the attachment of liga- 
ments. The trapezium articulates with four bones, the scaphoid, trapezoid, and the 
first and second metacarpal bones. 
Trapezoid Bone (os multangulum minus).—With 
the exception of the pisiform, this is the smallest of the 
carpal bones. Its rough palmar surface is small and 
pentagonal in outline. By a small oblong surface on 
its superior aspect it articulates with the scaphoid. 
Inferiorly, by a somewhat saddle-shaped surface, it 
articulates with the base of the second metacarpal. 
Separated from this by a rough V-shaped impression, is the surface on the outer 
side for articulation with the trape- 
zu; this appears as if obliquely 
grooved from before backwards and 
downwards. The internal facet for 
articulation with the os magnum is 
narrow from above downwards, and 
deeply curved from before backwards. 
The dorsal surface of the bone, which 
is rough and non-articular, is much 
larger than the palmar aspect. The 
mass of the bone, dorsally, is directed 
downwards and towards the ulnar side. 
The trapezoid articulates with four 
bones—the trapezium, scaphoid, os 
magnum, and the second metacarpal. 
Os Magnum (0s capitatum).—This 
is the largest of the carpal bones. Its 
palmar surface is rough and rounded. 
The superior portion of the bone forms 
the head, and is furnished with convex 
articular facets which fit into the 
hollows on the inferior surfaces of the 
scaphoid and semilunar; that for the 
latter is internal to and separated by 
a shght ridge from the scaphoid articular area. The inferior surface, narrow 
towards its palmar border and broad dorsally, is subdivided usually into three 
Triangnlu 
fibro-cartilage 
of wrist 
Semilunar 
Fic. 143.—THe RicHr CUNEIFORM BONE. 
Cuneiform 
Fic. 144.—THE RIGHT PISIFORM 
BONE. 
Seaphoia — 
Fic. 145.—Tut Ricut TRAPEZIUM. 
