1896.] 



MYOLOGY OF EODBNTS. 



103 



side of the nasal aperture. The zygomaticus rises behind and 

 below the eye and runs to the angle of the mouth. The orbicularis 

 oi'is is feeble, as tlio mouth never closes over the enormous lower 

 incisors, and the infra-labial muscles are hardly developed at all. 



Fig. 5. 



OILHTOR, MARIS 



ZYCOMATieuS.'AejjX^ 



Face-muscles of Bathyergus. 



This description applies to the other animals examined, with the 

 exception that a depressor labii inferioris can be made out, and 

 that tlie orbicularis palpebrarum is better developed than in the 

 Spalacidoe. The other facial muscles, especially the zygomaticus, 

 are more difficult to separate from the facial panuiculus. Windle, 

 however, made out a levator alas nasi, a dilatator naris, and a 

 levator labii iuferioris in Hydromys chrysogaster '. 



Bucoinaior. — The buccinator has the normal arrangement, 

 except in Cricetomys and Crieetiis : iu 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 Spalacidsp, 

 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 Ilystricomorphine and Sciuromorphine 

 types of this muscle have already been described. In the 

 Myomorpha the type is usually Sciuromorphine, but certain 



P. Z. S. 1887, p. 54. 



ir« 



