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Show 162 MR. F. G. PARSONS ON THE [Jan. 14, and runs down to be inserted, also by a narrow flat tendon, just external to the former and covering its insertion. This part is especially well marked in Heteromys. This arrangement, which is present in all the genera of the Muridae that I have dissected, shows that, as the two muscles coexist in the same animal, they cannot be homologous, and I a m now of opinion that the so-called Fig. 3. ANT. DEEP MAS. 1 ^pTricomcrrphm^. Deep dissection of Hamster's masseter. Fig. 4. POST.Sup. S-DEEP MAS. ,LEY. LAB. A-NTfSUP.MAS. '.ANT. DEEP MAS. Masseter of Heteromys. anterior deep part of the Sciuromorphiue masseter is an extension forward of the posterior superficial plane of fibres. The arrangement in the Spalacidae gives a clue to the w^ay in which the infraorbital slip appears ; in these animals it is very feebly marked, rises from the margins of the infraorbital foramen, and runs back to blend with the temporal instead of having an independent insertion opposite the anterior cheek-teeth. Facial Muscles.-These muscles are best developed in the Spalacidae, especially in Bathyergus. 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, corresponding to the feeble development of the eye. The levator labii superioris corresponds with the description of it in the other Rodents \ The dilatator naris rises deep to this and passes to the ' P. Z. S. 1894, p. 253. |
