DISCUSSION 177 



to this position. It can readily be seen that in most other 

 mammals, whose limbs are normally at right angles to the 

 body axis, different muscle action results. Regarding just 

 what this comprises we are usually in ignorance. A well 

 known case in point is that the upper portion of the serratus 

 magnus can be flexed in man while the arm is in any posi- 

 tion, but the lower part can be brought into use only when 

 the humerus is at an angle of more than 45 degrees to the 

 body. In the case of one of the lower mammals, whose 

 normal position of the limbs is different than in man, these 

 facts are hardly likely to be the same. 



A muscle may be a prime agent in one or two movements, 

 but it may also assist in varjing degree during a great 

 number of other movements. Also it is well known that a 

 muscle possible of two different functions may be paralysed 

 for one but not for the other. The next logical step from 

 this is to the deduction that a muscle may be capable of 

 certain action in one mammal for which it is normally 

 ''paralysed" or inhibited in another. 



As further illustrating differing functions of the same 

 muscle, it may be mentioned, as discussed later, that in a 

 mammal with tibia and fibula fused, the muscles which in 

 man are emploj-ed for supination and pronation of the lower 

 leg may, and in fact must, be used largely for a different 

 purpose. 



The principles involved in the lever action of the different 

 classes of muscles may be ascertained from numerous text 

 books, but they will not here be discussed. The investiga- 

 tion of the lever power of the various muscles would be of 

 much value in the present connection, but the attachments 

 of most of the muscles are relatively so broad that the 

 decision for an exact point of insertion would be largely 

 arbitrary, and especially in the case of a subject as small 

 as the wood rat, the necessary percentage of error in the 

 calculations would be so large as to render the results value- 



