MAMMALIA. 



they always deliver themselves in leaping from the 

 hoot's of the hind feet, they receive the whole weight 

 of the body upon the fore ones, which support it until 

 the hind feet are brought up, as the points from which 

 to take a fresh leap. This is often done with so 

 much rapidity, and the body projected to so great a 

 distance, that we cannot observe the bringing up of 

 the hind feet, or the rest upon the fore ones, while 

 this is performing ; but whenever we see an animal in 

 this kind of action, it appears always to have the fore 

 feet at full stretch in advance, and the hind ones 

 equally so in the rear, and our conception is that 

 it trips along upon the points of the hoofs, without 

 any flexure of the legs. This however is not the 

 case, for all the joints of the legs, the muscles of 

 the shoulders and haunches, and partially also the 

 spine, are brought into equally violent and rapid 

 action in this magnificent style of progressive mo- 

 tion. The spine, indeed, has but little flexibility 

 in such animals, because a flexible spine would shorten 

 the leap ; but still in as far as it admits of change of 

 flexure, the spine of these animals comes as much into 

 action during their violent motions as any other part 

 of their body. This bounding motion is therefore 

 only a higher style of galloping than that practised 

 by such an animal as the racehorse ; and when an 

 antelope bounds over the lofty bushes, its action does 

 not differ in kind from that of a hunter when he 

 clears a hedge or takes a lofty gate. 



The leaping animals, properly so called, walk with 

 difficulty and a hopping motion, even when their 

 pace is at the utmost, and never exhibit the steady 

 straight-forward pace of the true walkers. 



The leaping animals among the placental mam- 

 malia almost all belong to the order Rodentia, or the 

 gnawing animals. To these must be added the kan- 

 garoo among marsupial animals, which are the most 

 characteristic leapers among the whole, as well as the 

 largest in size. 



The placental leapers belong to three distinct 

 genera, of which, however, it is unnecessary to give a 

 particular account here. The first and least effective 

 are the hares, which run rather than leap, at least as 

 standing erect on the hind legs, and they differ from 

 the others in having the tail exceedingly short, and 

 of comparatively no use either in directing their mo- 

 tion or assisting to support them when they move. 

 The following cut will furnish an idea of the position 

 of the hare when moving up hill, the kind of ground 

 upon which her motions are by far the most effective. 



It will be seen from the cut that the fore legs are 

 very short and slender, as compared with the hind 

 ones, which last are the chief organs of motion; the 

 bound taken upon them extending at least three times 

 as far as any that could be taken on the fore legs. 



When the long hind legs are brought forward, the 

 rump is greatly elevated compared with what it is 

 when they are stretched out ; and this is the reason 

 why a hare when running appears to be constantly 

 elevating the white or under part of the tail. It 

 is unnecessary to enter into any further particulars of 

 the motions of the hare, because it is an animal with 

 which every body is very familiar ; we may mention, 

 however, that from the kind of food on which they 

 have sometimes to subsist, and the way in which they 

 have to arrive at it, hares have sometimes to use 

 their feet as a sort of imperfect hands, that is, they 

 have not only to bring them to their mouth in feeding, 

 but to use them in climbing up to gnaw the bark of 

 bushes and young trees, at the season when there is 

 no other food for them in the fields ; in order that 

 they may have the cross motion of the fore feet 

 necessary for bringing them to the mouth, they have 

 some sort of point of support to prevent the shoulders 

 from approaching each other, and thus defeating the 

 grasping motion ; and this is done by means of im- 

 perfect clavicles. Perfect clavicles are necessary for 

 the performance of a perfect cross motion ; but as 

 with the hare such a motion is only occasional, the 

 clavicles are not complete, and thus they do not inter- 

 fere so much with the running of the animal as they 

 would do if perfect. 



The next gradation of leapers are the small animals 

 vulgarly known by the name of jumping hares (Pede- 

 tes}. Only one species of this animal is known. It 

 is a native of Southern Africa, about the size of a 

 rabbit, and burrows deeply in the ground. Its fore 

 feet, which are very well formed as compared with 

 the hind ones, have five toes ; and it uses them both 

 as hands in conveying the food to the mouth, and in 

 digging the burrows which it inhabits. It is a noc- 

 turnal animal, and during the dry season it has to find 

 its food by reaching upwards. Many of the mice 

 have this property to a considerable extent. 



The third, and perhaps the most expert leapers 

 among placental mammalia, are the jerboas properly 

 so called, of which there are several species, inhabit- 

 ants of the dry countries in Northern Africa and 

 Western Central Asia. In them the fore legs are so 

 short in proportion to the hind ones, that they are 

 rarely brought to the ground when the animal walks. 

 The deficiency of the fore legs is to a great extent 

 supplied by the size of the tail, which is longer than 

 the body of the animal, and which serves to balance 

 it in an upright position as it jumps along, springing 

 from and alighting on the hind feet, the soles of which 

 are provided with very large pads by which its fall is 

 broken. 



The tail of the jerboa is merely a balancing instru- 

 ment, and it possesses no great muscular power, all 

 the vertebrae of that organ being long and slender, 

 and destitute of any processes to which powerful 

 muscles could be attached. It has therefore less 

 motion than the tails of many animals, which are far 

 shorter. From the point of its insertion being so far 

 from the ground, it derives, however, a considerable 

 lever power ; and as the animal folds its short fore 

 legs down on the breast when it leaps, and holds the 

 body in nearly an erect position, the hind feet come 

 to the ground again, almost directly under the centre 

 of gravity ; reckoning from the articulations of the 

 thigh bones, the hind legs are at least six times the 

 length of the fore ones; and there is a peculiar form- 

 ation in the central part of the hind foot, which, inde- 



