486 CAPE JUMPING HARE CHAP. 
Alactaga is much lke Fuchoreutes; it has five toes, a 
cylindrical tufted tail, the hairs at the end distichous, smooth 
incisors, and a premolar present in the upper jaw. It also 
differs from Huchoreutes by the much smaller auditory bulla as well 
as in the fact that the infra-orbital foramen has no separate 
passage for the nerve, which passage is to be distinguished in 
both Dipus and Huchoreutes. The best-known species is the 
‘Siberian Jumping Rabbit, A. jaculus. Beneath the ends of the 
three main toes of the feet are remarkable fan-shaped pads. In 
A, decumana the body and tail measure 7 and 10 inches re- 
spectively, the ears 2 inches. Platycercomys, a fourth genus of 
the family, is much less known and is to be differentiated from the 
last three genera by the fact that it has no premolars at all, the 
grinding tooth formula being thus $. The tail too is flattened 
and “lancet shaped.” It extends from Siberia to Nubia, and 
thus just enters the Ethiopian region. 
The above are the more typical Jerboas. There remain 
several forms which are not at all Jerboa-like in their way of 
life, but are nevertheless, on anatomical grounds, placed with 
them. Zapus, an American genus, with the exception of one 
Palaearctic species, is transitional in that its hind-legs are 
rather long, but there is not so much difference between them as 
in the typical Dipodidae. Sminthus is at the opposite extreme 
to Dipus. Its feet are short and of equal length; it climbs in 
trees, and may perhaps be looked upon as nearest of all Dipodidae 
to the ancestral form of the group. 
Fam. 8. Pedetidae——The genus Pedetes contains but one 
species, P. caffer, the Cape Jumping Hare. The animal suggests 
a large Jerboa in appearance on account of its jumping habits, 
the long hind-limbs, and the long tail. The length of a fair- 
sized example is some 17 inches, with a tail of the same length. 
The eyes and ears are large. The hands are five-fingered and 
the feet only four-toed, the hallux being of course the absent 
digit. In the skeleton it is interesting to note that the second 
and third cervical vertebrae are so close together that there can 
be no free movement; interesting because in Dipus the cervicals 
are actually ankylosed. The dorsal vertebrae are twelve. The 
small intestine is long, measuring 7 feet 4 inches, while the 
caecum is short, being only 8 inches long. The large intestine 
is 3 feet 10 inches long. The gall-bladder appears to be 
