196 ANATOMY OF THE WOOD RAT 



extended and these flexors therefore have great elasticity. 

 The ones with most proximal attachment to the shank are 

 probably of considerably less use in flexion of this segment 

 than in extension of the femur, but the more distal ones, by 

 virtue of their insertions and the position of the bones, can 

 exert great force in flexion of the lower leg, and such action 

 is of far more importance to this animal while running than 

 can the corresponding motion be to man. In fact, it may 

 play almost as important a part in this as does the extension 

 of the femur. It will, then, be seen that the direct flexors 

 concerned with this portion of the leg are extraordinarily 

 efficient, and much larger as well as more numerous than 

 are those of the forearm, the latter having less need for 

 strength. The indirect flexors the (gastrocnemii and plan- 

 taris), however, seem to operate verj^ slightly as such. As 

 the tibia and fibula are solidly fused, there can, of course, be 

 no pronation and supination of this segment. 



Also due to the fact that there can be no rotation of the 

 lower leg in Neotoma, and because articulation with the foot 

 is by a single bone instead of two, thus reducing play, only 

 a negligible amount of rotation of this, the fourth segment, is 

 possible. But the foot must assume a great variety of 

 positions, as any one will realize who has observed a wood 

 rat endeavoring to escape from a trap. Hence, necessary 

 rotation of the foot must be accomplished by a rotation of 

 the whole leg at the hip joint, and both the myological and 

 osteological features allow a great amount of such move- 

 ment. 



Possible supination exceeds the average in man, for it is 

 possible for the "ball" of the foot to be placed at an angle of 

 slightly more than 90 degrees to the horizontal. Pronation 

 also greatly exceeds what is possible in the foot of man, and 

 the "ball" of the foot, although of course not the heel, may 

 assume in this direction an angle of about 75 degrees to the 

 horizontal. Examination of a cleaned skeleton sheds little 



