I10 
RODENTS. 
distinctive features in the skull, more especially in the large size of the hinder 
part of the auditory bulla, into which it would be out of place to enter here. 

SKELETON OF JERBOA. 
The jerboas and their allies are mainly Asiatic 
and African forms, although there is one outlying 
species in North America, and a few range into 
Southern Europe. Most of the jumping kinds are 
inhabitants of open and dry districts, such as grassy 
steppes or sandy deserts; and approximate in colora- 
tion very closely to that of the ground on which 
they dwell. They form burrows in clayey or sandy 
soil, which are generally situated in the open plains, 
but sometimes among thicker or thinner bush-jungle. 
In habits they are mostly nocturnal, lying concealed 
in their burrows by day, and issuing forth to feed 
at night. Their nutriment consists of roots, berries, 
seeds, fruits, leaves, grass, and other herbage; but a 
few will also eat insects, small birds, and carrion. 
In feeding they sit in a half-erect posture upon their 
hind-quarters and tail, and convey the food to their 
mouth with the aid of their paws. Their move- 
ments are peculiar; the body being supported on 
the hind-limbs alone, perhaps aided, however, at times 
by the tail. In walking, the legs are moved alternately 
in the ordinary manner; in which respect these animals 
differ from kangaroos, which always hop. Progression 
at a more rapid rate is, however, always effected by a 
series of leaps from the hind-legs; the length of such 
leaps being generally very great in proportion to the 
size of the animal. Like all desert-haunting animals, 
the jerboas are extremely quick of hearing and long- 
sighted. Although generally silent, many of these 
animals have a kind of whining ery, which has been 
compared to that of a kitten. In the colder districts 
of their habitat, the species hibernate more or less completely; but they never 
lay up a store of provisions for winter use. 
The family may be divided into four main groups or subfamilies. 
THE JUMPING MOUSE. 
Genus Zapus. 
The so-called jumping mouse of North America (Zapus hudsonianus) is the 
typical representative of the first group of the family. It is characterised by the 
presence of four pairs of rooted cheek-teeth in each jaw, by the vertebre of 
the neck being entirely separate from each other, and by the long hind-limbs 
being furnished with five complete toes, of which the metatarsal bones are 
