376 MR. tt. I. POCOCK ON THE EXTERNAL 



The only genus of the group which has genuine cheek-pouches 

 is Cadogenys; Init near the edge of the cheek, just inside the 

 mouth, in CJiiiichilla I find a small integumental pocket on each 

 side. These do not seem large enough for the storage of food, 

 and I am unable to surmise what their function m;iy be. (Text- 

 fig. 4, E.) 



The cheek-pouches in Codogenys lie on each side of the maxillary 

 portions of the palate, mainly in front of the molar teeth, and are 

 associated with the well-known and unique structural peculiarity 

 of the skull from which the genus takes its name. The outer 

 wall of each pouch is the original skin of the cheek, which 

 infeiiorly passes downwards on to the face behind the corner of 

 the mouth. But this wall is entirely concealed from view 

 externally by the skin-covered, arched, laminate outgrowth of 

 the maxillary portion of the zygoma, which curves downwards 

 below the level of the palate and the molar teeth ; and this 

 lamina itself forms the outer wall of a hair-lined external cheek- 

 pouch the orifice of which lies on the face above and behind the 

 angle of the mouth. Thus the original wall of the cheek, 

 covered with hair externally and with moist mucous membrane 

 internally, forms a partition between the internal and external 

 cheek-pouches; aiid this partition, being pliable, can be thrust 

 by pressure from inside the mouth so as to bulge into the cavity 

 of the outer cheek-pouch so as to diminish its size and increase 

 to a corresponding degree the size of the internal cheek-pouch. 

 If the latter were packed full of food, the external pouch would 

 be practically obliterated ; but there would be no visible swelling 

 on the face, such as is seen in the case of monkeys, hamsters, and 

 other mammals provided with these food-receptacles, because of 

 the presence of the secondary cheek formed by the bony out- 

 growth of the zygomatic arch. (Text-fig. 5, A, B.) 



There can, I think, be no doubt that the internal cheek-pouches 

 are used for storing food, although I have never found any food 

 in them in dead specimens of Coelogenys. I attach no import- 

 ance, however, to this negative piece of evidence, because the 

 pouches of monkeys aie usually empty when they die. That the 

 external cheek-pouches are not used for storing food is also, in 

 my opinion, beyond doubt, because the fore feet of Ccelogenys are, 

 judging from tlieir structure, altogether unsuitable for thrusting 

 food into them. 



From the description above given, it will be evident that the 

 laminate expansion of the tnaxilla acts as an external shield to 

 the cheek-pouch when distended. But this affords no expla- 

 nation of the equally remarkable expansion of the jugal portion 

 of the zygomatic arch behind the cheek-pouch. 



Tke Ear. 



The ear in Hystrix and Atlierura is comparatively small, but 

 stands well up from the head with a tolerably evenly rounded 



