180 ANATOMY OF THE WOOD RAT 



cervical musculature. The neck may be lengthened or 

 shortened for particular reasons, or it may have to support 

 unusual weight, as in the moose or elephant. The muscles 

 of the neck often show great variation, of much value to the 

 anatomist, but such specialization is not easily correlated, 

 as a rule, with diverse modes of locomotion. Ordinarily the 

 muscles of the back are employed largely for static work, 

 as stiffeners of the vertebral column in the various positions 

 which the latter may assume. In the case of those mammals 

 capable of prodigious leaps the body acts as a fulcrum upon 

 which work the levers of the limbs, and its musculature may 

 be accordingly modified secondarily to a very significant 

 degree; or in such a long-bodied and short-legged animal as 

 the weasel the back-bone and its musculature may con- 

 stitute an important, primary aid to locomotion. The more 

 distal portion of the tail muscles in animals in which this 

 member is non-prehensile usually has few characters of 

 much interest to us. Save in the kangaroos and in aquatic 

 mammals, the tail is seldom used to exert real force of any 

 kind, but only as a balancer to maintain necessary equilib- 

 rium of its owner, and the muscles at the base of the tail 

 are used to perform the movements corollary to this. 



It is in the leg muscles that we should expect to find the 

 greatest direct indications of varied life habits, and sig- 

 nificant similarities in such as exhibit convergence toward 

 marked specialization of a particular nature. Few details 

 of an animal may be said to be unnecessary for its continued 

 existence, of course, but as concerns its own sum of charac- 

 ters, it is upon its ability to travel about in the manner most 

 suitable to its ecologic position that its survival as a species 

 chiefly depends. Therefore it is in the leg muscles, especially 

 of those mammals that are well fitted for particular modes 

 of locomotion, that we are primarily interested. 



Forty to sixty years ago there was much philosophical 

 discussion by such men as Agassiz, Oken, Owen and Wilder 



