118 ANATOMY OF THE WOOD RAT 



the shape of the palate and the precise conformation of the 

 mesopterygoid plates, but not to an extent easily expressed 

 by words. Teonoma usually has a sUghtly defined, medial 

 spine to the palate. There are also differences in the shape 

 of the audital bullae, those of Teonoma being least globular, 

 but the variation in relative size is slight. The styloglossal 

 process upon the inferior border of the auditory meatus is 

 well developed in all three, perhaps best so in Neotoma, 

 but the latter assertion is not corroborated by any appre- 

 ciable difference in the muscle itself. The pterygoid fossae 

 are narrowest in Homodontomys and deepest in Neotoma, 

 indicating stronger internal pterygoid muscles in the latter 

 animal. There is equal development of the fossa upon 

 either side of the basioccipital bone, from which originate 

 the longis capitis and rectus capitis anterior muscles, and of 

 the paroccipital processes. The latter serve for attachment 

 of the obliquus capitis superior, stylohyoid, and digastric 

 muscles, and especially in view of differences obtaining in 

 the last, these processes might be expected to exhibit greater 

 variation. 



So many muscles are attached to the rear of the skull that 

 the occipital varies individually in a very complex manner, 

 and perhaps the only safe subgeneric statement to make is 

 that in Teonoma the occipital surface is more prone to ex- 

 hibit an anterior inclination. The reason for this in the 

 present animal is obscure. In rodents this is popularly 

 accepted as a fossorial character, but as far as known 

 Teonoma is even less given to burrowing than are other 

 wood rats that do not show this development. 



The angularity and definition of the processes, especially 

 the medial spine, of the occipital increase with age, as is to be 

 expected, but the depth of the rectus fossae varies more with 

 the individual than with age. There undoubtedly occur in- 

 dications of differences in the development of the cervical 

 muscles, but they are so inextricably interwoven that it 

 seems unsafe to treat them in detail. 



