OSTEOLOGY 111 



majority of these, in the genus Neotoma, can be homologized 

 with those of the above mammals, but for others it has been 

 necessary to coin new terms. This has been done with 

 as much conservatism as possible, and wherever practi- 

 cable, these osteological names have been adapted to har- 

 monize with those of the muscles which are attached to the 

 respective parts. 



SKULL 



The accompanying illustrations give a better idea of the 

 form of the skull than can a description, and complete verbal 

 details of all the component bones is hardly necessary. 



A cursory examination of skulls showing similar age 

 development of the three subgenera compared seems to show 

 that in Teonoma the rostrum is longer, the braincase is 

 broader and shorter, and the zygomatic width is greater, 

 than in the other two. Similarly, one gains the impression 

 that the rostrum is longer, the braincase broader, and the 

 zygomatic width less in Homodontomys than Neotoma. 



A careful study of large series of each of these three ani- 

 mals would undoubtedly show trustworthy, though small, 

 average, relative differences in measurements. But such is 

 not the purpose of the present paper — it is for the com- 

 parison of the few specimens of each species, or rather sub- 

 genus, which one could be expected to dissect. Neither do 

 actual differences in real size of the three animals concern us 

 for the present purpose (osteology), and such are to be 

 ehminated in actual comparison wherever possible. 



Returning once more to apparent differences in the skull, 

 more careful study shows that most of these are in the nature 

 of optical illusions. After taking a dozen measurements of 

 half a dozen skulls of adults of each of the three animals and 

 reducing each measurement to percentage of the condylo- 

 basilar length, it is seen that the difference in relative size 

 in the three subgenera is so shght that it probably is not 



