OSTEOLOGY 121 



and reference to the myology shows that this is the case with 

 the sterno- and cleidomastoids. 



A summary of the cranial osteological differences, some of 

 which are obscurely or not at all related to the musculature 

 of the three animals, is as follows: The anterior extension 

 of the infraorbital plate of the maxillary process is shortest 

 in Teonoma; the dorsal line in profile is straightest in 

 Teonoma; most curved in Neotoma; the interorbital ridges, 

 separated by a sulcus, are heaviest in Teonoma; the audital 

 bullae are least globular in the same subgenus : the posterior 

 portion of the zygomatic arches are relatively most flaring 

 in Teonoma and least so in Homodontomys; the interptery- 

 goid fossa is broadest in Neotoma, and the pterygoid fossae 

 narrowest in Homodontomys; in Teonoma the palatals ex- 

 tend quite to the basi- and presphenoids, while in the other 

 two animals they do not, thus forming wide vacuities within 

 this portion of the pterygoid fossa — an excellent subspecific 

 character, but one which does not prove to be subgenerically 

 uniform; in Teonoma the post-palatal foramen consists of a 

 slight slit, in Neotoma it is more truly a foramen and in 

 Homodontomys it is largest. 



Teeth 



The incisors are a trifle broader and heavier in Teonoma 

 than in the other two animals. As is always the case in 

 rodents, they grow from persistent pulps throughout the life 

 of the individual. 



The molariform teeth are moderately brachyodont, or 

 short crowned, but to a less extent than in such a genus as 

 Peromyscus, in this respect being fairly intermediate between 

 the latter and such an animal as Evotomys. 



The length of the tooth row, as figured in percentage of the 

 condylobasilar length, is far more variable individually 

 and with age than subgenerically. In fact, this is the case 

 to such a degree that it can not be determined whether there 



