1G2 MB. r. O. PARSONS ON THE [Jau. 14, 



and runs down to be inserted, also by a narrow flat tendon, just 

 external to tbe former and covering its insertion. Tbis part is 

 especially well marked in Ileteromys. This arrangement, which is 

 present in all the genera of the Muridie that I have dissected, 

 shows that, aa the two muscles coexist in the same animal, they 

 cannot be homologous, and I am now of opinion that the so-called 



Fis. 3. 



XnT. DEEP MAS. 



I H^sTncomar/ih/'ne; 



Deep dissection of Hamster's niasseter. 



Fig. 4. 



,LLV. LAB. 



Post. Sup 

 j^deep mas.-' 



ANTrSUP.MAS. ' '^•"•T. DEtP MAS. 



■ScitLTomoTp/n'rrei. 



Maa-setor of Heteromys. 



anterior deep part of the Sciuromorphiue masseter is an extension 

 forward of the posterior superficial plane of fibres. The arrange- 

 ment in the Spalacidaj gives a clue to the way in which the infra- 

 orbital slip appears ; in these animals it is very feebly marked, rises 

 from the margins of the infraorbital foramen, and runs back to 

 blond with the temporal instead of having an independent insertion 

 opposite the anterior cheek-teeth. 



Facial Muscles. — These muscles are best developed in the 

 SpalacidiB, especially in Dathyergus. In this animal the frontalis 

 is continuous dorsally and laterally with the superficial panniculus, 

 and the muscles of the small auricle are extensions from this. 

 The orbicularis palpebrarum in Bathyergus is very small, corre- 

 sponding to the feeble development of the eye. The levator labii 

 superioris corresponds with the description of it in the other 

 Eodents". The dilalator naris rises deep to this and passes to the 



' P. Z. S. 1894, p. 253. 



