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JERBOA
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JERBOA , properly the name of an Arabian and See also:North See also:African See also:jumping rodent mammal, Jaculus aegyptius (also known as Jaculus, or Dipus,. jaculus) typifying the See also:family Jaculidae (or Dipodidae), but in a wider sense applied to most of the representatives of that family, which are widely distributed over the See also:desert and semi-desert tracts of the Old See also:World, although unknown in See also:Africa See also:south of the See also:Sahara. In all the more typical members of the family the three See also:middle metatarsals of the See also:long See also:hind-legs are fused into a See also:cannon-See also:bone; and in the true jerboas of the genus Jaculus the two lateral toes, with their supporting metatarsals, are lost, although they are See also:present in the alactagas (Alactaga), in which, however, as in certain allied genera, only the three middle toes are functional. As regards the true jerboas, there is a curious resemblance in the structure of their hind-legs to that obtaining among birds. In both See also:groups, for instance, the See also:lower See also:part of the hind-See also:leg is formed by a long, slender cannon-bone, or metatarsus, terminating inferiorly in triple condyles for the three long and sharply clawed toes, the resemblance being increased by the fact that in both cases the small bone of the leg (fibula) is fused with the large one (See also:tibia). It may also be noticed that in mammals and birds which See also:hop on two legs, such as jerboas, kangaroos, thrushes and finches, the proportionate length of the thigh-bone or femur to the tibia and See also:foot (metatarsus and toes) is See also:constant, being 2 to 5; in animals, on the other See also:hand, such as See also:hares, horses and frogs, which use all four feet, the corresponding lengths are 4 to 7. The resemblance between the jerboa's and the See also:bird's See also:skeleton is owing to See also:adaptation to a similar mode of existence. In the See also:young jerboa the proportion of the femur to the See also:rest of the leg is the same as in See also:ordinary See also:running animals. Further, at an See also:early See also:stage of development the fibula is a See also:complete and See also:separate bone, while the three metatarsals, which subsequently fuse together to See also:form the cannon-bone, are likewise separate. In addition to their long hind and See also:short fore limbs, jerboas are mostly characterized by their silky coats—of a fawn See also:colour to harmonize with their desert surroundings—their large eyes, and long tails and ears. As is always the See also:case with large-eared animals, the tympanic bullae of the See also:skull are of unusually large See also:size; the size varying in the different genera according to that of the ears. (For the characteristics of the family and of its more important generic representatives, see See also:RODENTIA.) In the See also:Egyptian jerboa the length of the See also:body is 8 in., and that of the tail, which is long, cylindrical and covered with short See also:hair terminated by a tuft, to in. The five-toed front limbs are extremely short, while the hind pair are six times as long. When about to See also:spring, this jerboa raises its body by means of the hinder extremities, and supports itself at the same See also:time upon its tail, while the fore-feet are so closely pressed to the See also:breast as to be scarcely visible, which doubtless suggested the name Dipus, or two-footed. It then leaps into the See also:air and alights upon its four feet, but instantaneously erecting itself, it makes another spring, and so on in such rapid See also:succession as to appear as if rather flying than running. It is a gregarious See also:animal, living in considerable colonies in burrows, which it excavates with its nails and See also:teeth in the sandy See also:soil of See also:Egypt and See also:Arabia. In these it remains during See also:great part of the See also:day, emerging at See also:night in See also:search of the herbs on which it feeds. It is exceedingly shy, and this, together with its extraordinary agility, renders it difficult to See also:capture. The See also:Arabs, however, succeed by closing up all the exits from the burrows with a single exception, by which the rodents are forced to See also:escape, and over which a See also:net is placed for their capture. When confined, they will gnaw through the hardest See also:wood in See also:order to make their escape. The See also:Persian jerboa (Alactaga indica) is also a nocturnal burrowing animal, feeding chiefly on See also:grain, which it stores up in underground repositories, closing these when full, and only See also:drawing upon them when the See also:supply of See also:food above ground is exhausted (see also JUMPING See also:MousE). (R. Additional information and CommentsThere are no comments yet for this article.
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