14 ANATOMY OP THE WOOD RAT 



etc). Mammals living among tall grass or brush that is 

 not dense have tails slightly longer for their respective groups 

 {Microtus townsendi, Peromyscus m. sonoriensis, etc.). 

 Rodents frequenting moderately heavy brush usually have 

 tails that are slightly longer still (Microtus mordax, which 

 frequents situations more brushy than do most voles; 

 Peromyscus h. rowleyi, etc.), while mammals of the heaviest 

 brush or forests, which may also be partly arboreal, have the 

 longest tails {Peromyscus m. oreas, Neotoma (Homodontomys) 

 fuscipes) . 



Thus, Neotoma albigula has the shortest tail of any of the 

 three subgenera studied, which undoubtedly means that 

 this member has not been used to as great an extent as a 

 balancer while the animal was climbing into and among 

 bushes and trees. Homodontomys has much the longest tail 

 of the three, indicating that it is consistently used as a 

 balancer while its owner is clambering about in precarious 

 situations. The tail of Teonoma is negligibly longer than 

 that of Neotoma albigula, but in the former this member is 

 heavily clothed with long hairs, and it is known that this 

 character answers the same purpose as greater length. 

 Theoretically it may be accepted that the hairy tail of 

 Teonoma is of as much aid to its owner in negotiating the 

 rocks and cliffs of its habitat as is the long, terete tail of 

 Homodontomys. Whether in practice it is actually more 

 efficient in such situations or less so we shall probably never 

 know. 



There is some variation in the relative size of the hind foot 

 of the three species. In Homodontomys this member is 20.2 

 per cent of the length of the head and body; in Neotoma it is 

 17.7 per cent; and in Teonoma, 20.4 per cent. This is also 

 in accordance with the line of reasoning offered in the case 

 of the tail. The hind foot of Neotoma, which is the most 

 generalized of the three, is relatively shortest, and the toes 

 are also shorter and narrower. In Homodontomys, living in 



