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. 
‘FRONTALIS, 
DILATOR NARIS. : 
Lev. casi, 
SS —S 
“ ~ 
Zycomarticus Ne y™ 
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 the orbicularis palpebrarum is better developed than in the 
Spalacide. The other facial muscles, especially the zygomaticus, 
are more difficult to separate from the facial panniculus. Windle, 
however, made out a levator ale nasi, a dilatator naris, and a 
levator labii inferioris in Hydromys chrysogaster’. 
Buceinator.—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 Spalacide, 
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. 
Ingastric—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. 8. 1887, p. 54. 
11* 
