164 ANATOMY OF THE RABBIT. 
acting on the forearm. The distal extremity of the bone is formed 
by an epiphysis, similar to but much longer than that of the radius. 
It is immovably articulated with the radius, and its tip is formed 
by a blunt styloid process (processus styloideus), which is 
articulated with the triquetral bone of the carpus. 
The elbow-joint is formed by the trochlea and capitulum of the 
humerus in conjunction with the semilunar notch of the ulna and 
the corresponding articular surface of the head of the radius. It is 
a hinge-joint, or ginglymus, permitting motion in one plane, 7.e., 
extension and flexion of the forearm. The trochlear surface of the 
humerus, however, has a slight spiral trend, the anterior portion 
being medial in comparison with the posterior portion. 
Through the immovable articulation provided by the respective 
proximal and distal ends of the bones, and also through the inter- 
osseous ligament, the radius and ulna are unable to change their 
positions with respect to one another; in other words, the radius is 
unable to rotate on an axis formed by the ulna, the fore foot being 
fixed in a position comparable to that of pronation in the human 
hand (cf. p. 65). 
THE CARPUS. 
The carpus (Fig. 68) comprises nine small elements, the wrist 
or carpal bones (ossa carpi), which are interposed between the 
forearm and the digits. They are arranged in two main rows, 
namely, a proximal row, the elements of which are articulated 
with the radius and ulna; and a distal row, the elements of which 
are articulated with the five bones of the metacarpus. Enumerated 
from the medial side of the wrist laterad, the proximal row contains” 
four elements, namely, the navicular, lunate, triquetral and 
pisiform bones. The navicular and lunate are articulated 
with the distal extremity of the radius; the triquetral with the 
styloid process of the ulna. The pisiform bone lies on the ventral 
surface of the extremity of the ulna, and is therefore not exposed 
to the dorsal surface of the wrist. The distal row contains five 
elements, namely, the greater multangular, lesser mult- 
angular, central, capitate, and hamate bones. The first, 
second, and fourth are in association respectively with the first, 
second, and third metacarpals. The central bone lies to the 
se 
