318 



PKOI". r. G. PAESONS ON THE 



Muscles of the Head and Neclc. 



Temporal. — This muscle is quite small, as is usual in rodents. 

 The three parts described by Kunstler * — parietal, temporal, and 

 zygomatic — are present, but not very clearly defined. The muscles 

 of opposite sides do not nearly meet in the mid-line ; but it must 

 be remembered that the specimen is that of a very young animal, 

 and there is reason to believe that, with the growth of the teeth, 

 the masticatory muscles become more developed and the temporal 

 occupies more of the side of the cranium. 



Masseter. — This is a muscle of great interest. In previous 

 papers t I have pointed out that the bysfcricomorphine and 

 sciuromorphine types of masseter are quite distinct, and it is well 

 known that this difference causes a complete alteration in the 

 shape of the skull. In most squirrel-like rodents no part of 

 the masseter passes through the infraorbital foramen, but a 

 special bundle, which has been spoken of as the sciuromorphine 

 anterior deep part, occupies a nearly vertical groove in front 

 of the zygomatic process of the maxilla. In the porcupine- 

 like rodents a considerable part of the masseter, called the 

 hystricomorphine anterior deep portion, passes through the 



Fig. 1. 

 M^SSETtH. CUT. 



N\A>S>S^ cut./ 



ANTS DEEP PART oP 

 MASiSETtK. , 



The Masseter of Anomalurus. 



o-reatly enlarged infraorbital foramen; while the mouse-like 

 rodents show the transition between these two arrangements, 

 and often, as in the case of the Hamster (Cticetus frumen- 



* Annales des Sciences Naturelles, ser. 7, t. iy. 

 t P. Z. S. 1894, p. 261, and 1896, p. 159. 



ser. 7, t. iy. p. 150. 



