1282 



THE RODENTS 



the molars marked by transverse enamel folds. The skull, as shown in the accom- 

 panying figure of the skeleton of the jerboa, is characterized by the shortness of the 

 brain case, and the very large size of the apertures in front of the eye sockets for 

 the passage of the nerves supplying the face. There are also other distinctive fea- 

 tures 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. 



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 coloration 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 thin- 

 ner 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 ani- 

 mals have a kind of whining cry, which has been 

 compared to that of a kitten. In the colder districts of 

 their habitat, the species hibernate more or less com- 

 pletely, 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 characterized by 



SKELETON OF JERBOA. 



