Indeed, despite the fact that they present much diversity of habit - some being arboreal, as the squirrels, many of which are provided with expansions of skin or parachutes on which they glide from tree to tree; some cursorial, as the hares; others jumpers, as the jerboas; others fossorial, as the mole-rats; and others aquatic, as the beavers and waterrats - no important structural modifications are correlated with such diversity of habit.
In the Jaculidae the metatarsals are greatly elongated, and in some of the species, as jerboas, they are welded together.
In general habits and appearance these animals recall large jerboas, from which group they are, however, distinguished by the four pairs of rooted cheek-teeth, the premolars being as large as the molars, and the latter having one outer and one inner enamel-fold.
- The next Myoxoidea, or dormice, mouse group, have the three sections of the order, namely, the Dipodoidea, or jerboas, and Myoidea, or the following characteristics in common.
In the typical jerboas, Jaculus (or Dipus), ranging from North Africa to Persia, Russia and Central Asia, there are only three hind toes, the incisors are grooved, and the premolars are generally wanting.