THORACIC LIMBS. 71 
oblong plate bearing on its proximal surface a semicircular 
ridge which crosses it diagonally. The proximal end of the 
bone articulates with the scapholunar. Its distal end articulates 
with the third metacarpal except near its ventroulnar angle, 
where it articulates with the fourth metacarpal. Its ulnar sur- 
face articulates with the unciform. Its radial border articulates 
with the trapezoid, the third metacarpal, and, by two facets, 
with the second metacarpal. 
Trapezord. (Os multangulum minus BNA) (Fig. 51, ¢).— 
The trapezoid is somewhat wedge-shaped, with the apex of the 
wedge pointing ventrad. Its proximal side articulates with the 
scapholunar, its distal side with the second metacarpal, its ulnar 
side with the os magnum, and its radial side with the trapezium. 
Trapezium. (Os multangulum majus BNA.) (Fig. 51, @). 
—The trapezium has the form of a triangular prism curved into 
a semicircle. The convex face looks proximad and articulates 
by its ventral half with the scapholunar. The ulnar surface 
articulates with the second metacarpal dorsally, and ventrally 
with the trapezoid. Its radial surface articulates with the first 
metacarpal. 
Bones of the Hand or Manus (Fig. 51, 1-5).—The Meta- 
carpals. Metacarpus.—The metacarpals are the five bones of 
the palm of the hand; they are numbered from one to five, 
beginning with the thumb. They are cylindical elongated bones 
with enlarged ends. The distal end is called the head, and the 
proximal end the base. Each head bears a hemispherical 
articular facet which is marked over its ventral half by a 
prominent smooth ridge. The surface dorsad of the ridge 
articulates with the proximal head of a phalanx. The ridge 
and the surface at its sides are for a pair of sesamoid bones. 
The first metacarpal (1) is the shortest. Its head is oblique, 
and it articulates by the ulnar half of its proximal surface with 
the trapezium (@); by the radial half with the radial sesa- 
moid (4). 
The second metacarpal (2) is marked on the proximal part 
of its dorsal surface by an oblique groove passing from the 
radial side distad to the ulnar side. The base articulates with 
the trapezoid (e). The ulnar surface of the proximal end 
