190 ANATOMY OF THE WOOD RAT 



The weakness of the smaller muscles of the fore foot and 

 digits, coupled with the fact that the pollexis non-functional, 

 implies only a moderate amount of facility in digital move- 

 ments. Flexion and extension of the latter are adequately 

 strong, but as a true hand, the extremity of the fore leg is 

 not highly accomplished. 



The functional length of the fore Umb in the genus Neo- 

 toma is only about two-thirds that of the hind leg. The 

 former member is used to a considerable extent as a tool 

 during the normal activity of the animal, this constituting 

 an important secondary use. Its primary use is, of course, 

 for locomotion, but even during this function it need do 

 little but support the anterior portion of the body, while 

 the hind limbs can furnish practically all of the driving 

 power if necessary. As the importance during locomotion 

 of the fore limbs decreases, so will their size (unless stimu- 

 lated by other hard work), and this, naturally, is followed 

 by a compensating increase in locomotional importance and 

 relative size of the hind limbs. 



The pelvis must be considered as, functionally, the first 

 segment of the hind limb, corresponding to the scapula, 

 although the former is immovably fused to the vertebral 

 column. Strength of a certain sort could be secured by an 

 increase in the size of the muscles without such fusion, but 

 rigidity of support is perhaps requisite to the efficiency dis- 

 played by the hind limbs in swift locomotion and the proper 

 performance of many of the other feats which these members 

 are called upon to execute in daily life. As the pelvis is 

 immovable, all adduction, abduction, and rotation of the 

 leg must be through the femur, which is rendered possible 

 by its ball-and-socket joint with the pelvis. Practically all 

 muscles governing such actions must therefore arise from 

 the pelvis or its vicinity, and most of them are inserted upon 

 the femoral segment, although several extend to the lower 

 leg. 



