2 ANATOMY OF THE WOOD RAT 



anatomy of the cat or of man, which is now necessary if one 

 is to have confidence in his results. 



The object in undertaking the present investigation was 

 to gain a comprehensive understanding, from a practical 

 viewpoint, of certain portions of the gross anatomy of a 

 medium-sized, generalized, cricetine rodent. Attention has 

 been paid to correlating the groups of limb muscles and to 

 the effects of their functions and stresses upon the bones 

 of the skeleton. This work was done in order that it might 

 constitute a basis upon which the writer might investigate 

 to better advantage the convergence exhibited by mammals 

 of diverse affinities toward types highly specialized for 

 certain definite modes of life. The present paper constitutes 

 part one of this program. It was made comparative in order 

 that it might be of greater technical value, and that we might 

 learn more regarding the anatomical variation to be ex- 

 pected within those closely-related groups of mammals 

 which we term subgenera. Since illustrations are pre- 

 requisite to anatomical work of a satisfactory character, a 

 series of these has been prepared which it is hoped will 

 prove entirely adequate. 



It would have been highly desirable to have investigated 

 at least the more critical points in the anatomy of every 

 species and a number of subspecies of the genus Neotoma. 

 It is practically certain that a new phylogenetic arrangement 

 considerably better than the one now in use could thus 

 be obtained. It is not unlikely that there exist anatomical 

 differences between some of the more distinct species of the 

 subgenus Neotoma that might serve to differentiate these 

 subgenerically. It would take years, however, to secure the 

 material necessary for such an undertaking. It should 

 therefore be emphasized that the present program can not 

 definitely settle the subgeneric standing of the different 

 groups of wood rats. Comparisons are used solely to 

 ascertain and indicate anatomical differences that may be 



