114 ANATOMY OF THE WOOD RAT 



curved, with a slight depression along the anterior portion 

 of the cranium, which may also be present to a very slight 

 extent in Homodontomys. The dorsal line of the skull in 

 Neotoma is most curved. The entire skull of Teonoma pre- 

 sents a more angular appearance, chiefly due to the angu- 

 larity of the zygoma and the heavy temporal ridging. The 

 interorbital ridging is heaviest in this animal as well, and in 

 fact, in all three it is better defined than is the temporal 

 ridging proper. The interorbital ridging is not the direct 

 result of any muscular stimulus. It may be a fortuitous 

 development^ — the result of crowding — or a more anterior, 

 secondary result of development of the temporal muscles. 

 The anterior division of the temporal muscle is indicated 

 as being appreciably strongest in Teonoma, and least so in 

 Homodontomys. This is so to an even greater extent in the 

 case of the posterior division of the temporal. In Homodon- 

 tomys and Neotoma there is no means of distinguishing the 

 point where one division of the temporal ends and the other 

 begins, save by the slight change in direction of the temporal 

 ridging. In old specimens of Teonoma, however, the fossa 

 of the anterior division of the temporal is separated from 

 that of the posterior by a well marked ridge, running cranio- 

 laterad from the temporal ridging. In such animals the 

 lambdoidal crest is also developed to an unusual degree; 

 but this is also attributable to the development of certain 

 of the cervical muscles. Another indication of the great 

 strength of the temporals in Teonoma is the fact that they 

 are situated more mediad — the distance between them is 

 less — than in the two others, and to this extent the origins 

 occupy more surface. Similarly the posterior divergence 



Fig. 24. Details of the skull and mandible of Teonoma. A, Lateral 

 aspect of the left side of skull, showing muscle attachments. B, Occipital 

 aspect of skull: muscle attachments at right, osteological details upon the 

 left. C, Medial aspect of the left side of mandible, showing muscle attach- 

 ments. 



