184 ANATOMY OF THE WOOD RAT 



The diagrammatically simplified plan of musculature for 

 each segment of a limb is a long, direct flexor and extensor, 

 inserted upon the bone and originating from the second 

 segment above; a short, direct flexor and extensor, inserted 

 upon the bone and originating from the segment next above; 

 and an indirect flexor and extensor, originating upon the 

 segment next above and inserted upon the one next below 

 (see fig. 36). In actual practice, of course, the simplified 

 scheme for the fourth and fifth segments, with the several 

 tarsal and digital elements, would be much more complex 

 than this. No such schematic plan for adductors and 

 abductors can be given, for although all joints are capable 

 of extension and flexion, comparatively few allow extensive 

 adduction and abduction. 



So far as I am aware, the above plan is never met with in 

 actual practice, for anatomical complications, following 

 the need for complex actions, has been forced far beyond 

 such simpHcity. In many cases it is possible to state which 

 are the primary long, short, and indirect flexors or extensors, 

 but usually the musculature has become so specialized, 

 in even the lowest mammals, so split up and changed, that 

 muscles which really should be classed as accessory may 

 often be as important as true primary ones, while the 

 functions of others have changed entirely; so that in the 

 present stage of the technique on the subject, it behooves 

 one to be conservative in making statements. A qualifying 

 phrase of caution can not accompany each item hereafter 

 mentioned, without proving tedious, however, so it must be 

 understood that the muscle facts and actions given are 

 merely what seems to be so, from an examination of the 

 material. The following tables have been prepared after a 

 careful study of the positions of the muscles in the genus 

 Neotoma, with due regard to the functions of the same mus- 

 cles in man and the cat. Their functions, as stated, repre- 



