XV STRUCTURE OF JERBOA 485 
There is even the same ankylosis of the neck vertebrae. We 
find, moreover, the same association of long-legged and shorter- 
legged forms that characterises the Heteromyidae. 
The typical genus Dipus is a smallish quadruped with long 
naked ears and a long tail. The ten 
: “ee Cc! 
species are all Palaearctic in range. The 
fore-limbs are short and five fingered, and BLE 
the short pollex has no claw; the hind- 
limbs are excessively long and only three- 
toed. The bony structure of these limbs 
is remarkable. The three metatarsals are 
elongated almost like those of a bird, and 
are ankylosed together. The digits have 
long phalanges which alone reach the 
ground as the animal hops. It is a curious 
fact, and one not so easily identifiable with 
the way of life, that the neck vertebrae of 
this genus are ankylosed together with the 
exception of the atlas, which is free; the 
: n 
arrangement is precisely hke that of the 
Sperm Whale. The last vertebra is, how- ait 
, wayayee a a Fia. 239.—Bones of right pes 
ever, sometimes free. The J erboas not a eronnoal Tinie usqiviiie 
only leap but they burrow, and their strong x#. a, Astragalus; c, 
caleaneum; c?, middle 
3 
incisors are said to be used in burrowing Clare On geuter 
through stony ground. Theyare eaten by cuneiform; cb, cuboid; 
; m, navicular; I-IV, first 
the Arabs, and are, or have been, called” 46 -tourth toes. | (From 
Daman Israel, z.e. Lamb of Israel. In Flower’s Osteology. ) 
D. hirtipes the body and tail measure respectively 45 and 7 
inches. The hind-feet have a tuft of long hairs below. Mr. 
W. L. Sclater’s newly-founded genus Ewuchoreutes’ is somewhat 
more primitive in its characters than is Dipus. The general 
form is the same, with long ears and a long tail. But there 
are five toes to the hind-limb, the two lateral ones though 
nailed being much shorter than the middle three. It has a 
“Jong pig-like snout,” and the tail is cylindrical as in most other 
Jerboas, with a tuft of longer hairs at the end. The incisor 
teeth, grooved in Dipus, are here smooth, as in Alactaga. The 
species was probably obtained “in the sandy plains round the 
city of Yarkand.” 
' Proc. Zool. Soc. 1890, p. 610. 
