200 SKELETON OF THE DOG 
is produced to a blunt point (Processus styloideus ulne). It articulates with the 
ulnar carpal distally, and has a convex facet on its dorso-medial aspect for the radius. 
The proximal end of the radius unites with the shaft at six to eight months, the 
distal at about one and a half years of age. The olecranon and the distal end of the 
ulna fuse with the rest of the bone at about fifteen months. 
The carpus comprises seven bones—three in the proximal row and four in the 
distal. The numerical reduction in the proximal row is apparently due to the 
fusion of the radial and intermediate, constituting a large bone (radio-intermediate) 
which articulates with almost all of the 
Olecrancn distal surface of the radius and with the 
bones of the distal row. It projects promi- 
nently on the volar surface of the carpus. 
Processus anconeus ‘Lhe ulnar carpal is long; it articulates with 
the radius and ulna above and the acces- 
Semilunar notch sory behind; below it rests on the fourth 
ZX Fovea capituli carpal and is prolonged downward to ar- 
ticulate with the fifth metacarpal also. 
The accessory is cylindrical, constricted 
in its middle and enlarged at each end; the 
anterior extremity articulates with the 
ulna and ulnar carpal bone. The first car- 
pal is the smallest bone of the lower row; 
it articulates with the second carpal later- 
Shaft of ally‘and the first metacarpal distally. The 
radius a 
second carpal is wedge-shaped, the base be- 
ing posterior; its proximal surface is con- 
vex, and its distal is coneave and rests on 
the second metacarpal. The third carpal 
is somewhat like the second; its distal sur- 
face is concave and articulates chiefly with 
the third metacarpal. The fourth carpal 
is the largest of the row; it articulates with 
the fourth and fifth metacarpals. Two 
small bones or cartilages may be found on 
the volar surface at the junction of the two 
b rows, and a third small bone articulates 
with the medial side of the radio-inter- 
mediate.! 
Five metacarpal bones are present. 
Carpal articular The first is much the shortest; the third 
eurlace and fourth are the longest, and are about 
one-fifth longer than the second and fifth. 
pattie dren GOR ta cE Ge Lie haar The fifth is the widest at the proximal end 
and brachialis muscles; b, groove for tendon of exten- 20d is slightly shorter than the second. 
sor carpi obliquus, They are close together above, but diverge 
somewhat distally; the first is separated 
from the second by a considerable interosseous space. They are so arranged as to 
form a convex dorsal surface and a concave volar surface, which corresponds to 
the hollow of the palm of the hand in man. Each consists of a shaft and two ex- 
tremities. The shaft is compressed from before backward. In the third and fourth 
it is almost four-sided, in the second and fifth three-sided, in the first rounded. 
The proximal ends (Bases) articulate with each other and with the corresponding 
Shaft of ulna 
Interosseous 
space 
Styloid process 
of ulna 
Fig. 220.—Lerr Rapius anp Utna oF Doc; Meprau 
View. 
1The third bone was termed the phacoid in the cat by Strauss-Durckeim, and is regarded 
by some authors as the vestige of an additional digit, the prepollex. 
