MOTION. 



463 



Fig. 246. 



leg moves rather oftener during the same pe- 

 riod in trotting than in walking, or as 6 to 5. 

 The velocity acquired by moving the legs in 

 pairs, instead of consecutively, depends on the 

 circumstance that in the trot each leg rests on 

 the ground during a short interval, and swings 

 during a long one, whilst in walking each leg 

 swings a short, and rests a long period. The 

 undulations arising from the projection of the 

 trunk in the trot are chiefly in the vertical 

 plane ; in the walk they are in the horizontal. 



In fig. 246, as designed by Bewick, and 

 adapted to our purpose, we observe that the 

 vertical line passing through the base of sup- 

 port, lies not only behind the centre of gravity 

 of the horse, but also of the centre of the mass 

 of the rider, consequently the anterior le^s 

 will bear much the greatest proportion of the 

 burthen. 



The gallop. The gallop may be divided 

 into three kinds, which may be distinguished 

 by the number and order in which the feet 

 happen to reach the ground. When the horse 

 begins the gallop on the right, the left hind leg 

 reaches the ground first; the right hind and 

 left fore legs next, simultaneously, and the 

 right fore leg last; this is termed the gallop of 

 three beats. In the gallop where the four legs 

 strike the ground successively, the left hind 

 foot reaches the ground first, the right hind 

 foot second, the left fore foot third, and the 

 right fore foot fourth ; this is the gallop of four 

 tieats, but it is not the kind of movement 

 adapted for great speed.* The gallop wherein 

 the legs follow the same order as in the trot, 

 that is, the left hind and right fore feet reach 

 the ground simultaneously, then the right hind 

 and left fore feet ; is the order in which horses 

 move their feet in racing, where their greatest 

 speed is required, and is called the gallop of 

 two beats.-^ In the amble, the two legs on one 

 side rest on the ground, and propel the centre 

 of gravity forwards, whilst those on the oppo- 

 site side are raised and advanced, and on 

 taking a new position on the plane of motion, 

 the former pair are raised and advanced in a 

 similar manner: these successive actions are 

 accompanied by a considerable lateral motion. 

 The amble is the pace peculiar to the Giraffe : 



* The gallop of four beats is often denominated 

 " the Canter." 

 t See Sainbell. 



in the horse it is only effected bj artificial 

 training. Borelli has erroneously described the 

 order of the motions of the feet of the horse in 

 walking; he states that the fore and hind feet 

 on the same side move first, and then the fore 

 and hind feet on the opposite side : these 

 views, however, differ from the order as de- 

 scribed by Aristotle,* and they have since 

 been opposed by Barthez and Miiller, whose 

 opinions coincide with those which, after 

 repeated observations, have been here intro- 

 duced. In the gallop, the centre of gra- 

 vity moves in a vertical plane, and describes the 

 path of a projectile. The space passed over 

 on the plane of motion is equal to the hori- 

 zontal velocity of the centre of gravity multiplied 

 by the time.f According to Sainbell, the cele- 

 brated horse, Eclipse, when galloping at liberty, 

 and with its greatest speed, passed over the 

 space of twenty-five feet at each stride or leap, 

 which he repeated 2J times in a second, being 

 nearly four miles in six minutes and two se- 

 conds. The race-horse, Flying Childers, was 

 computed to have passed over eighty-two feet and 

 a half in a second, or nearly a mile in a minute. 

 Sainbell has given the geometrical proportions 

 of Eclipse, together with the angles of in- 

 clination and range of motion of the joints of 

 the four extremities. He states that a consi- 

 derable angle of inclination of the shoulder- 

 joint, as well as an angular disposition of the 

 limbs, are essentially necessary for great speed. 

 Sir C. Bell4 however, states, " that the speed 

 of a horse depends on the strength of his loins 

 and hind-quarters, and what is required in the 

 fore-legs is strength in the extensor tendons ;" 

 but surely this hypothesis cannot be correct, or 

 the brewer's dray-norse would be the fleetest. 

 The horse is one of the most useful and most 

 perfectly organized quadrupeds, combining 

 great strength with speed. The length, strength, 

 and angular disposition of the bones of the 

 legs, the power of the muscles, the structure of 

 the joints, the lengthened metatarsal and me- 

 tacarpal bones, the consolidation of the pha- 

 langes, and the structure of the expanded foot, all 

 conspire to perfect the geometrical proportions 

 of this valuable quadruped. 



Having now given in detail the various 

 movements of the horse, we shall briefly pass 

 to the other orders of Mammalia. 



Marsupialia, In the Kangaroo, we observe 

 a greater disproportion between the length of 

 the anterior and posterior extremities than is 

 found in any other quadruped, the length of the 

 legs to that of the arms being as 38% to 17$ 

 inches, or rather more than two to one. This 



* After the right of the fore feet they move the 

 left of the hind feet. Afterwards they move the 

 left of the fore feet and right of the hind feet. 

 See Taylor's Aristotle on the Progressive Motion of 

 Animals, chap. xiv. 



t See eq. 1. 



J Library of Useful Knowledge, Art. Animal 

 Mechanics. 



These measures are taken from a skeleton in 

 the Huntrrian Museum. Some variation will 

 occur in the absolute length of the extremities, 

 arising from the age and magnitude of the animal ' 

 but the ratio of the length of the extremities in the 



