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Show 1896.] MYOLOGY OF RODENTS. 163 side of the nasal aperture. The zygomaticus rises behind and below the eye and runs to the angle of the mouth. The orbicularis oris is feeble, as the mouth never closes over the enormous lower incisors, and the infra-labial muscles are hardly developed at all. Fig. 5. |F R.ONTALI3 . Face-muscles of Bathyeryus. This description applies to the other animals examined, with the exception that a depressor labii inferioris can be made out, and that the orbicularis palpebrarum is better developed than in the Spalacidae. The other facial muscles, especially the zygomaticus, are more difficult to separate from the facial panniculus. Windle, however, made out a levator alae nasi, a dilatator naris, and a levator labii inferioris in Hydromys chrysogaster 1. Buccinator.-The buccinator has the normal arrangement, except in Cricetomys and Cricetus: in the former animal I was unfortunately unable to examine the face owing to its damaged condition; in the latter the muscle is prolonged into a pouch which runs back along the side of the neck as far as the scapula, at its blind extremity a muscular fasciculus is attached to it, which runs backward to the posterior thoracic spines parallel to the posterior border of the trapezius, of which it seems a part, as it is supplied by a continuation of the spinal accessory nerve coming out of the trapezius. The action of this muscle would be to draw back the pouch and possibly to assist in emptying it. Pterygoids.-The description of these muscles already given applies to the arrangement in the Myomorpha. In the Spalacidae, especially in Bathyergus, the large anterior superficial part of the masseter is inserted into the inner surface of the mandible above the insertion of the internal pterygoid, so that the latter seems to stand out in a more isolated manner than is usually the case. Digastric.-Distinct Hystricomorphine and Sciuromorphine types of this muscle have already been described. In the Myomorpha the type is usually Sciuromorphine, but certain 1 P. Z. S. 18S7, p. 54. 11* |
