JERBO'A, or GERBOA (from Ar. yarbfi', flesh of the back and loins, oblique descending muscle jerboa : so called from the great muscular development of the hind legs). A small rodent of the genus Dipus and family Dipodithe, related to rats and mice, and remarkable for its kanga roo-like characteristics. (See Plate of MicE AND JERDOAS. ) In true jerboas the fore legs, more used as hands than as feet, are very small and have five toes, while the hind limbs are exces sively long and strong, and have only three toes, of which the middle (TIM) is prolonged. The tail is long, cylindrical, covered with short hair, and tufted at the end. The jerboas are inhabi tants of sandy deserts and wide grassy plains in Asia and in Eastern Europe and North Africa. They are burrowing animals, nocturnal, and feed upon roots. seeds. herbage, insects, birds' eggs, and the like, and where numerous greatly damage the grain crops. Their great legs enable them to flee from danger in enormous leaps, but when undisturbed they walk upright. one foot after the other, and do not hop like a kangaroo. They
hibernate in the colder countries. but do not lay up stores as do many mice. The best known species is Dipus _Egyptiens, of the North African plains. It is from six to eight inches long be sides the tail, which is longer than the body.
Another group of jerboas. principally Asiatic, is distinguished by having five toes on the hind feet, and includes the alacdaga (Alactaga Ikea mana), an animal as large as a rat and one of the most characteristic animals of the Kirgheez steppes. Several lessor species of the same genus exist, and the great Siberian jumping rabbit of the genus Euchoreutes is another relative. Finally, the familiar jumping mouse (q.v.) of the United States is one of this family. as also are the rat-like rodents of Northern Europe and Ash of the genus Sminthus. whose legs are all of nearly equal length. and whose habits are arboreal. These more regular forms are supposed to have least departed from the ancestral type. Consult Blanford's hooks upon the zoidogy of India, Persia. and Abyssinia.