SACCOMYIDZ—DIPODOMYIN #®—DIPODOMYS. Dao 
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 incisors. 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 Geomyid@; 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 Gvomyide—those 
of Geomys hispidus tor instance. The opening is crescentic; 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 Joosely around to the side of 
the under jaw near its middle. 
The whiskers are extremely numerous, and some of them are 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. Qthers grow in the usual site, and the longest of these usually exceed 
