CHANGES FOR ADAPTATION IN THE MOLE 351 
(fig. 8, el) on the distal side and the tuberculum minus (tm) on 
the proximal side, is for the passage of the flexor muscles of the 
forearm. These muscles have their origins in a cavity of the 
humerus just under the articulation for the scapula (f). The 
origins of the extensor muscles of the forearm is at the proximal 
and posterior margin of the humerus just posterior to the facies 
articularis scapulae (f). 
There are four articular surfaces on the humerus. A proximal 
one, caput humeri (figs. 8, 9, 10, ch) which articulates with the 
clavicle, is somewhat oval in outline, and has almost the uni- 
form convexity of a cylinder. It is 6.8 mm. in a horizontal and 
4.5 mm. in a vertical direction. This surface being so much 
greater than that of the clavicle (30.6 sq.mm. vs. 13.2 sq.mm.) 
with which it articulates rather indicates that there may pos- 
sibly be a sliding movement in an anteroposterior direction at 
this joint. 
A second articular surface, facies articularis scapulae, (f), 1s 
situated on an eminence on the dorsal side near the proximal 
end, a short distance posterior to the caput humeri. It is almost 
almond-shaped and measures 3.8 mm. in a lateral direction and 
1.5 mm. in a direction parallel with the axis of the body. As its 
name indicates, it is the articular surface for the scapula. 
The third and fourth articular surfaces are located at the 
distal end of the humerus. They are the trochlea humeri (¢r), 
the articular surface for the ulna, and the capitulum humeri (c), 
the articular surface for the radius. The trochlea humeri is 
shaped like a slightly bent cylinder whose length is 2.7 mm. and 
diameter 1.5 mm. ‘There is a depression, the fossa coronoidea 
(fig. 10, fc) on the ventral side just proximal to the articular 
surface. It provides room for the coronoid process of the ulna 
in extreme flexion. A depression, the fossa olecrani (fo), similarly 
situated on the dorsal surface, furnishes room for the process of 
the olecranon in extreme extension of the forearm. 
The bones of the forearm also show some marked modifica- 
tions. They are both very strongly formed and reinforced. 
They are relatively short and thick compared with the general 
mammalian type. The radius, instead of the long cylindrical 
JOURNAL OF MORPHOLOGY, VOL. 34, NO. 2 
