BONES OF THE THORACIC LIMB 149 
The first carpal is absent. The second and 
The fourth carpal is a 
articulates with the ulnar carpal only. 
third carpals are fused to form a large quadrilateral bone. 
smaller quadrilateral bone. 
The metacarpus consists of a large metacarpal and a lateral small metacarpal 
bone. The large metacarpal bone (Mc. 3 + 4) results from the fusion of the third 
and fourth bones of the foetus, and bears evidences of its double origin even in the 
adult state. The shaft is shorter than in the horse, and is relatively wider and 
flatter. The dorsal surface is rounded, and is marked by a vertical vascular 
groove connecting two canals which traverse the ends of the shaft from before 
backward. The volar surface is flat and presents a similar but much fainter groove. 
The borders are rough in the proximal third. The proximal end bears two slightly 
concave facets for articulation with the bones of the lower row of the carpus; the 
medial area is the larger, and they are separated by a 
ridge in front and a notch behind. The lateral angle 
has a facet behind for the small metacarpal bone. The 
medial part of the extremity has anterior and posterior 
tuberosities. The distal end is divided into two parts 
by a sagittal notch. Each division bears an articular 
surface similar to that in the horse, but much smaller. 
The medullary cavity is divided into two parts by a ver- 
tical septum which is usually incomplete in the adult. 
The small metacarpal bone (Me. 5) is a rounded rod 
about an inch and a half (ca. 3.5 to 4 cm.) in length, 
which lies against the proximal part of the lateral bor- 
der of the large bone. Its proximal end articulates with 
the latter, but not with the carpus. The distal end is 
pointed. 
Four cartilaginous metacarpals are present in the early foetal 
state, viz., the second, third, fourth, and fifth. The second com- 
monly either disappears or unites with the third; sometimes it 
develops asa small rod of bone. The third and fourth gradually 
unite, but can be cut apart at birth. Each has three centers of 
ossification; the proximal epiphysis fuses with the shaft before 
birth, the distal at two to two and one-half years. 
Four digits are present in the ox. Of these, two— 
the third and fourth—are fully developed and have 
METACARPAL 
Fic. 150.—Lerr 
three phalanges and three sesamoids each. The second 
and fifth are vestiges and are placed behind the fetlock; 
each contains one or two small bones which do not ar- 
ticulate with the rest of the skeleton. 
The first phalanx is shorter and narrower than in 
the horse and is three-sided. The interdigital surface is 
flattened and its volar part bears a prominence for the 
attachment of the interdigital ligaments. 
large, and is somewhat compressed from side to side. 
Bones oF Ox; Front View. 
THe SmaLt BoNE HAS BEEN 
Movep LaTeratty. 
1, Metacarpal tuberosity; 2, 
vascular groove; 3, 3’, foramina; 
4, 4’, condyles; 5, articular facet 
of fifth (small) metacarpal bone. 
The proximal extremity is relatively 
The articular surface is con- 
cave from before backward and is divided by a sagittal groove into two areas, of 
which the abaxial one is the larger and higher. 
articulation with the sesamoid bones. 
separated by a deep depression. 
especially in the dorso-volar direction. 
Behind these are two facets for 
The volar surface bears two tuberosities 
The distal extremity is smaller than the proximal, 
Its articular surface is divided by a sagittal 
groove into two convex facets, of which the abaxial one is decidedly the larger. 
There are depressions on either side for ligamentous attachment. The bone con- 
sists at birth of two pieces—the distal end and the fused shaft and proximal ex- 
tremity. Union occurs at one and one-half to two years. 
The second phalanx is about two-thirds of the length of the first and is dis- 
