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Show 160 MR. F. G. PARSONS ON THE [Jan. 14, The following is a list of the animals dissected for the first part of the present paper:- Myoxus dryas. Gerbillus shawi. Cricetus frumentarius. Cricetomys gambianus. Microtus amphibius. My odes lemmus. Mus decumanus. Mus rattus. Mus barbarus. Rhyzomys badius. Georychus capensis. Bathyergus maritimus. Heteromys longicaudatus. Also Lepus timidus and Lepus cuniculus for the sake of comparison. Accounts of the muscles of other animals by various authors have been used and their sources acknowledged in the text. Muscles of the Head and Neck. Temporal.-In all the Myomorpha the three parts of the temporal are more closely fused than they are in the Sciuromorpha, in this respect resembling the Hystricomorphine arrangement. In the Water-Vole the parietal part of the muscle is very large and arises from the temporal fascia, as well as the parietal, maxillary, and frontal bones. It runs down as a flat tendon to be inserted, opposite the anterior molar teeth, into the mandible. The anterior deep part of the masseter, after coming through the infraorbital foramen, joins this tendon. Fig. 1. PA«VETA.V. |wrtof TEMP. ,J ^ M P. ANT P.MAS. POST DEELP MAS, Masticatory muscles of Vole. In the Myoxidae and Muridae the muscles of opposite sides are separated by an interval which is often, as in Mus rattus, of considerable extent. In the Spalacidae, on the other hand, the two muscles rise close together, and the superficial layer described by Allen 2 is distinct and rises by aponeurosis from the sagittal crest. These animals, moreover, bear out the statement in Bronn's 1 Pr. Acad. Nat. Sc. of Philadelphia, vol. iii. p. 385. |