Jerboa, the principal old-world representative of the rodent subfamily dipodinae, characterized by greatly developed hind legs for taking long leaps, diminutive fore legs, long hairy tail, and large infra-orbital foramen. The best known species is the Egyptian jerboa (dipus AEgyptius, Licht.). The incisors are slender and sharp, the upper ones grooved, two above and two below; the molars, 3/3-3/3, are complex, furnished with roots; the head is large, with prominent eyes, moderate pointed ears, and silken whiskers 6 in. long. In external conformation it somewhat resembles the kangaroo, having an elongated body thickest behind, the posterior limbs very much larger than the anterior; the neck is very short, and the six lower vertebrae are frequently found united together; the metatarsus consists of a single bone; there are five toes on the short fore feet, and three on the posterior, armed with obtuse claws; the tail is long, with hairs set in two rows, and tufted at the end; it is not thick at the base, as in the kangaroo, though it is used to sustain the body in the act of leaping. The body is about as large as a rat's, of a fawn color above and white below, the black tuft of the tail white tipped.

From its generic name, which signifies two-footed, it has been supposed that the jerboa walks entirely on the hind feet; but the animal walks upon four feet, resorting to its prodigious leaps only when alarmed; when about to spring, it raises itself on the end of the hind feet, with the support of the tail, the fore feet close to the breast; the body comes down on the fore feet, but is elevated again so quickly that it appears constantly in the air. All the species are clavicu-lated, and carry their food to the mouth with the fore paws; they pass the winter in burrows in a state of lethargy; they are difficult to keep in captivity, even in their own climates; the females are generally the largest, and have six or eight young. The Egyptian species lives in troops in northern Africa, most abundantly in the sandy regions and ruined places of Egypt; it extends into Syria and Arabia, and as far north as the Caspian sea; it is restless and timid, and can be taken only by surprise. The Arabians take jerboas alive in their burrows; their flesh is eaten by the Egyptians, and their soft and shining fur is valued by them. The food of the jerboas is exclusively vegetable, and they are said never to drink.

The largest species is the scirtetes jaculua (Wagn.), about 9 in. long, found in the steppes between the Donetz and the Don and in the Crimea; this is the alak-daagha of the Mongols. The fur is soft, yellowish fawn varied with grayish brown above; the under parts, interior of limbs, end of nose, and crescent on the nates are white. The general appearance and habits are as in the common species; they become lethargic both under slight cold and great heat; the food consists of succulent plants, roots, fruits, insects, and, it is said, of small birds and of each other; they dig very rapidly into the earth, and live in burrows with many openings; their swiftness is such that it is difficult to overtake them even on horseback; their flesh is also esteemed as food. - To this family also belong other jumping rodents, often called jerboas. Among them is the jumping hare of South Africa (pedetes Cafer, Illig.), with molars 4/4-4/4 without roots, long ears, five toes on the fore feet and four on the hind, with long claws; the posterior limbs and tail are long, the latter tufted. It moves by great leaps, and sleeps by day; it is as large as a rabbit, of a fawn color, with the end of the tail black.

In North America is the jumping mouse (jaculus Hudsonius, Zimm.), about 10 in. long, of which the tail is more than half; the color is red-brown, darker on the back, the sides and under parts white. It is found as far north as the Great Slave lake. The molars are 4/3-4/3; the hand has four fingers with a rudimentary thumb, hind feet five-toed, hind legs and tail very long, the latter thinly haired; upper incisors grooved longitudinally in front. For full details on this genus, see vol. viii. of the reports of the Pacific railroad survey.

Egyptian Jerboa (Dipus AEgyptius).