OSTEOLOGY 113 



greater than is individual variation. In dorsal view, the 

 rostrum of Teonoma seems longer because of its greater 

 actual length, because it holds a uniform width practically 

 to its end, and because the anterior extension of the septa of 

 the maxillary processes of the zygomae are shorter: in ven- 

 tral view, because the incisive foramina are longer. Actually 

 it seems to average only two per cent longer in this sub- 

 genus than the others. The rostrum of Neotoma seems 

 shorter than of Homodontomys because it tapers more 

 toward the tip. 



The braincase of Teonoma is relatively the shortest. This 

 makes it appear broader, which illusion is strengthened by 

 the appearance of great width presented by the posterior por- 

 tion of the zygomatic arches. This is caused chiefly by the 

 fact that the anterior portion of the zygoma is narrowest in 

 Teonoma, is slightly wider in Neotoma, and broadest in 

 Homodontomys; but relatively speaking, the difference in the 

 width of the braincase or in total zygomatic breadth is too 

 little to be taken into serious account. 



The only positive indications of muscular attachments 

 upon the rostrum are the shght process just ventrad of the 

 cranio-ventral border of the infraorbital foramen, from 

 which originates the masseter superficiahs, of equal develop- 

 ment in all three animals, and the infraorbital fossa, situated 

 craniad to the foramen of the same name, from which arises 

 the infraorbital head of the masseter major. 



As previously mentioned, the anterior portion of the 

 zygomatic process of the maxilla does not extend so far 

 craniad in Teonoma, and this means that the entire septum 

 is smaller. In the tw^o others it is to all intents equal in size. 

 This indicates that the ectal portion of the masseter major 

 is relatively weaker in Teonoma, and a further indication of 

 this may be the narrowness in that subgenus of the anterior 

 portion of the zygomatic arch. 



In profile the dorsal line of the skull of Teonoma is less 



