DISCUSSION 211 



are somewhat larger in Teonoma but the insertions of these 

 are not so situated as to leave osteological record of the fact. 



Subgeneric variation in the relative length of the different 

 metacarpal bones is hardly of great functional importance. 

 Judging by the tendons of insertion, the extensor digitorum 

 communis and flexor digitorum sublimis are shghtly most 

 efficient in Teonoma. In this subgenus only is there no 

 falciform. 



A comparison of the ler>gth of the innominate to the body 

 length gives a percentage that is least in Homodontomys 

 and uniform in the other two, while its comparison with the 

 functional leg length, which is probably less desirable, gives 

 just the opposite result. Otherwise there is no subgeneric 

 variation in the innominate; but there is much individual 

 variation of some functional importance. In this connec- 

 tion the points of chief interest to us are the cranial portion 

 of the ilium and the inferior tuberosity of the ischium. The 

 former shows much individuality in its precise conformation, 

 correspondingly influencing chiefly the origins of the gluteus 

 superficiaHs anterior and the two lesser gluteal muscles. 

 Variation encountered in the inferior tuberosity of the 

 ischium consists of this point being a varying distance 

 either craniad or caudad of the superior tuberosity, and 

 hence, influencing by this much the leverage of several 

 muscles that act upon the femur and shank. 



The functional length of the hind leg, as calculated by the 

 formula already given, is 66.5 per cent of the length of the 

 body vertebrae in Homodontomys, 75 in Neotoma, and 73 in 

 Teonoma. This shows that whatever the cause, the sub- 

 genus that is most inclined to be arboreal in habits has 

 either the shortest hind leg, or else that the body is the 

 longest of the three. That the leg — and arm — of this animal 

 is the shortest seems doubtful to the writer, for this is not a 

 character usually developed by an active mammal with 

 scansorial prochvities. That the length of its body verte- 



