STRAIGHTENING OF THE LIMBS IN LOCOMOTION. 63 



the propulsion derived from the long leg will exceed that from the short 

 one in nearly the proportion which their lengths bear to each other. This 

 conclusion is in accordance with M. Marey's statement {see p. 4), that 

 muscles of speed are long muscles. Besides this, physiology teaches us 

 that the thicker muscles are, the slower, other things being equal, do they 

 contract on becoming stimulated ? We should content ourselves with taking 

 a broad view of this subject ; for conditions vary so much in individual cases, 

 that it is not safe to dogmatise on it. 



I need hardly say to those of my readers who have followed me so far, 

 that the greater the ability to straighten the leg, the higher will be the speed 

 of propulsion, and vice versa. Hence, if a horse is, for instance, unable from 

 peculiarity of conformation to straighten his hocks (a condition called " sickle- 

 hocks," see PI. 49), he will not be so fast as he would have been, had he 

 greater freedom in these joints. We may test the truth of this principle in our 

 own selves; for if, when swimming in a bath {see p. 58), we wanted to touch 

 and turn, but were unable to straighten our knee on account of an injury 

 or from some other cause, we would be capable of giving only a comparatively 

 poor kick-off. The great beauty of a "straight dropped hind leg" {see PI. 

 51), in the horse, as a conformation favourable to speed, will again be 

 alluded to on p. 236. 



The action of the fore limb in raising the forehand, which is essential for 

 the regulation of the position of the centre of gravity in locomotion, is also 

 dependent on its difference of length when bent and when straightened out. 

 It is manifest that this difference is mainly due to the action of the shoulder 

 joint and of the fetlock. Hence, oblique shoulders and sloping pasterns are 

 " points " of speed and of leaping power. If the shoulder-blade and pastern be 

 already upright, the limb will be capable of but slight extension. 



In heavy draught, full straightening out of the limbs is not desirable ; for 

 the last part of this action is accomplished at a great mechanical disadvan- 

 tage, to which I have alluded on page 56. At present it is sufficient to 

 compare the action of the limbs to that of the oars of a boat, in which the 

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

 angles to the length of the boat ; the remainder of the propulsive effect 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 five hours. The cart-horse, when in heavy 



