MYOLOGY OF AISTOMALUEUS. 319 



tarius)*, both the sciuromorphine and hysfcricomorphine anterior 

 deep parts of the muscle are found in the same individual. 



Anomalurus differs from all the sciuromorphine rodents I have 

 hitherto examined in having a small anterior deep portion of the 

 masseter passing through the infraorbital foramen, as ia many of 

 the Myomorpha, and this arrangement I cannot help regarding 

 as a myomorphine tendency on the part of the animal. 



Depressor mandibula (Digastric). — The great difference between 

 the Seiuromorpha and Myomorpha on the one hand, and the 

 Hystricomorpha on the other, is that in the former suborders this 

 muscle is really digastric, and the tendons of opposite sides are 

 connected across the middle line by a fibrous arcade with its 

 convexity forward ; from this convexity the anterior bellies sprmg 

 in such a manner that the mesial borders of the two are in 

 contact in the middle line, and the anterior attachments of these 

 anterior bellies are close to the symphysis mentit. In the 

 Hystricomorpha, on the other hand, the muscle does not deserve 

 the name of digastric — the division between the anterior and 

 posterior bellies is only indicated by a few tendinous fibres on 

 its surface, there is no tendinous arcade, and the anterior attach- 

 ment is some distance from the symphysis^. Anomalurus agrees 

 entirely with the first-mentioned arrangement. 



Transversus mandibulce. — This muscle connects the two halves 

 of the mandible, just behind the symphysis, lying deep to the 

 depressor mandibulse and superficial to the mylohyoid ; it is 

 present in all the Myomorpha and Seiuromorpha except Castor. 

 In Anomalurus it is well developed. 



Sterno-cleido Mastoid. — The sterno-mastoid and cleido-occipital 

 elements of this compound muscle are present in Anomalurus, 

 the former running from the presternum to the base of the 

 paroccipital process, the latter from the inner half of the clavicle 

 to the curved line of the occipital bone ; as is always the case in 

 rodents, the spinal accessory nerve passes deep to both parts. In 

 many rodents the cleido-occipital portion is often overlapped by 

 the clavicular fibres of the trapezius, but this arrangement is not 

 confined to any one suborder, and it does not exist in Anomalurus; 

 but I do not at present regard, the sterno-cleido mastoid as of 

 much value from a classificatory point of view. 



* See figs. 2 &3, P. Z. S. 1896, pia. 161, 162. 

 t See fig. 1, P. Z. S. 1894, p. 2.55. 



I See fig. 9, Journ. of Anat. & Physiol, vol. xxxii. p. 439. 



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