CHANGES FOR ADAPTATION IN THE MOLE 358 
at the elbow, is approximately that of a hollow cylinder. Its 
surface is greatly increased on the distal side by the processus 
coronoideus and on the proximal side by a well-marked process 
from the olecranon. ‘This articular surface lacks only about 90° 
of forming a complete hollow cylinder. As may readily be seen, 
this permits forceful movements of the humerus with the fore- 
arm in any degree of flexion or extension, without probability of 
dislocation at the elbow. Some 3 or 4 mm. from the distal end 
the ulna approaches most nearly a cylindrical shape. From 
this point distally it rapidly widens to 5 mm. at the end in the 
same plane as the distal extremity of the radius. This wide 
expansion articulates with the os triquetrum and os pisiforme. 
Thus at the wrist both the bones of the forearm are flattened in 
the same plane as that of the manus, which is also the plane of 
extension and flexion of the forearm. The total width of these 
two articulations at thewrist is9.4mm. This is thus reduced to a 
simple hinge-joint. The proximal joint is, in my opinion, also a 
hinge-joint. The combined width of the ulna and radial articu- 
lations at the elbow is 5.5 mm. Since both the proximal and 
distal joints of the forearm are hinge-joints, it is obviously impos- 
sible for these species to execute a rotary movement of the 
manus similar to that in man. In the giant golden mole (Chryso- 
chloris trevelyani) Parsons (’01) claims that the hand can be 
rotated one-fourth of a circle. He states that this is possible 
because the proximal projection of the radius at the elbow is 
absent. It seems to me that the articulation of the ulna and 
radius at the wrist would also have to be different from that of 
Sealops and Scapanus to make this movement possible. 
There are eight carpal bones, an os centrale being present. 
These are indicated in figure 13. Besides these carpal bones, 
there are two sesamoid bones, the os pisiforme (p) and the os 
falciforme (Rs). The os pisiforme is attached to the distal end 
of the ulna at the edge of the wrist on the exterior surface. It 
has a hook-like projection extending toward the palmar surface. 
This doubtless assists in confining the tendons of the digits to the 
wrist region. The os falciforme or radial sesamoid is a long, 
narrow, sickle-shaped bone measuring 11 mm. long, 1.2 mm. thick, 
