SACCOMYID^E— DIPODOMYIN^E— DIPODOMYS. 533 



the animal, there is none of that preponderance of organization of the hinder 

 parts witnessed in the Kangaroo, with its massive haunches and enormous tail; 

 the whole body is equally slender, the leaping power being manifested in the 

 enlargement of the hind limbs alone; the tail, too, is slender throughout. 



The head is distinguished from the body by a well-defined cervical con- 

 striction. The broad high occipital region dips suddenly down to the nape. 

 The upper corners of the head, upon which the ears rest, are elevated and 

 wide apart; the top of the head has in general a triangular shape, tapering 

 from each ear to the snout with but slight swelling in the orbital region, and 

 is quite flat across, with the most gentle longitudinal curve in the frontal 

 region, and nearly straight nasal profile. The muzzle is acuminate and much 

 produced, appearing longer still in consequence of the remarkably small 

 retreating chin. The muzzle is entirely hairy, excepting a small nasal pad ; 

 this shows a median depression, but there is no cleft of the upper lip, the 

 whole of which is thickly clothed with stout hairs, that form a dense fringe 

 drooping over and concealing the superior iucisors. The lower lip is thick- 

 ened and densely hairy; and there is also a hairy commissure of the upper 

 lip behind the superior incisors, so that these teeth are shut out of the true 

 (mucous- lined) buccal cavity. For the rest, the lips seem to come together 

 vertically instead of horizontally, closing the oral aperture sideways, though 

 of course the buccal cavity or mouth proper shuts as in ordinary mammals. 

 All this is essentially the same as in the Geomyida ; and further, as in these 

 last, there is a great pouch on each side of the head, entirely disconnected 

 with the mouth, formed of a duplication of ordinary integument, hairy through- 

 out. These sacs will admit the first joint of one's little finger; they run the 

 whole length of the head, but not beyond to the shoulder. In relative 

 capacity, they about equal the least developed pouches of Gcomyidce — those 

 of Geomys hispidu^ for instance. The opening is cresccntic ; the inner limb 

 of the semilune being the skin of the jaws, while the outer limb is a free 

 fold or border arising on the side of the snout half-way between nostrils and 

 incisors and a little back of both, and curving loosely around to the side of 

 the under jaw near its middle. 



The whiskers are extremely numerous, and some of them arc very long. 

 A bunch of short fine ones springs from, the extremity of the snout, on each 

 side, by insensible lengthening of the fringe of hairs that, clothe the upper 

 lip. Others grow in the usual site, and the longest of these usually exceed 



