52 MECHANISM OF EQUINE LOCOMOTION. 



practically useful work is finished after the oais have passed the line at right 

 angles to the length of the boat ; the remainder of the propulsive efifect being 

 obtained by a wasteful expenditure of force. Consequently, an increase of 

 speed is procured by an amount of work that is greatly out of proportion to 

 the result. Thus, to double the speed during a certain period of time, it may 

 be necessary for the horse to do five or six times the amount of muscular 

 exertion. For instance, it may be more fatiguing for a horse to go twenty 

 miles in one hour, than fifty miles in fiYt hours. The cart-horse, when in 

 heavy draught, moves his load with his hind limbs in a moie or less bent 

 condition (Fig. 91), which will give his hind-quarters the crouching appear- 

 ance which must be familiar to us all. Sloping pasterns from a load-pulling 

 point of view are objectionable in the cart-horse ; for the more oblique they 

 are, the greater is the mechanical disadvantage at which they work (p. 57). 

 Sloping shoulders, also, from the same point of view, aie undesu'able. 



Action of the Muscles which extend the Vertebrae.— When 



a horse prepares to kick, he, as a general rule, lowers his head and arches 

 his loins (" puts his back up "), by doing which he relieves his hind-quarters 

 of weight and puts it on his foie hand. When, on the contrary, he prepares 

 to rear, he raises his head and neck and more or less hollows his loins, so as 

 to lighten his fore hand and put more weight on his hind-quarters. If we 

 examine Figs. 123 and 124 of the canter, Figs, 133 to 137 of the gallop, and 

 Figs. 195 to 199 of the leap, we shall see that the muscles which enable a 

 horse to rear, greatly aid the forward reach of the fore legs in the canter and 

 gallop. Also, the heavier the fore hand, the greater difficulty will they have 

 to raise it. In the leap, they assist the leading fore leg in raising the 

 fore hand. If the horse carries a rider, these muscles will have an increased 

 amount of work to do on account of extra weight being put in front, and will 

 tire in a proportionately rapid rate. On examining the drawings of horses in 

 Chapter XII. at the various paces, we shall see that the faster the movement, 

 the more will these muscles be taxed, on account of the greater distance of 

 the centre of gravity from the hind feet, during the period one or both of the 

 hind limbs support and propel forward the weight of the body. Hence we 

 find that to gallop fast or to jump "big," a horse must have good "rearing 

 muscles" which consist principally of those that straighten the hock, draw 

 back the thigh, and extend the vertebrae of the loins. These muscles also 

 help to "lighten" the fore hand in the flying trot and fast " pacing," in both 

 of which there is a period of suspension, which will vary in length according 

 to the weight that is on the fore hand. From these considerations I may lay 

 down the law that the faster the speed required, the stronger should the 

 " rearing muscles " be. The pair of them (one on each side) that is most 

 readily noticed, is the loin muscles, which in the ox constitute the upper cut 

 of a sirloin, and which, in the horse, we may see just behind the cantle of the 

 saddle, I need hardly say that the heavier the shoulder, the sooner will these 

 muscles become tired ; the shorter will be the stride ; and the slower will be 

 the pace. Consequently, horses for fast work ought to have light shoulders. 



