46 MECHANISM OF EQUINE LOCOMOTION. 



CHAPTER VIII. 



MECHANISM OF EQUINE LOCOMOTION. 



Displacement of the Centre of Gravity — Manner in which Propulsion is effected 

 by the Limbs — Direction of Propulsion, and Distance through which the 

 Centre of Gravity of the Body is moved~-Comparative Speed in the Action 

 of the Lmibs — Action of the Muscles which extend the Vertebrae — Width 

 between each respective Pair of Legs as affecting Speed — Effect of Insecurity 

 of Equilibrium on Speed — Fatigue from the various Paces — Action of the 

 Head and Neck in Locomotion — Mechanism of the Fetlock Joint — Mechanism 

 of the Hock Joint. 



The remarks made undei: this heading should be taken in connection with 

 those in the following five chapters. Some which are here given are necessary 

 for the proper comprehension of the movements of the horse in his various 

 paces ; but others, in order that they may be understood, have been kept 

 back, until the paces and draught have been discussed. 



Displacement of the Centre of Gravity.~The actions which 

 give rise to locomotion in the horse may be summed up as follows : — 

 Advancement of a limb in order to bring a new base of support under the 

 centre of gravity. Let us suppose that the man represented in Fig. 19 is 

 standing with one foot advanced more than the other. His base of support 

 {a b) will then be the area bounded by his feet and the lines joining them at 

 each side. As long as the perpendicular (/) dropped from the centre of 

 gravity falls within the base of support, the equilibrium of the body will be 

 maintained. If the man, in this example, brings the centre of gravity of 

 his body forward by straightening his left ankle joint, so that the perpen- 

 dicular from the centre of gravity shall fall beyond the base of support 

 (Fig. 20) ; it will be evident that iix order to prevent the body from failing, 

 he will have to bring the rear leg (which in this case is the left one) beyond 

 the perpendicular dropped from the centre of gravity (Fig. 21). Precisely 

 the same actions take place when the horse starts from the halt into the 

 walk ; for by the straightening of one or both hind legs, he brings the centre 

 of gravity of his body beyond the toe of the most advanced fore foot, with 

 the result that the other fore leg has to be carried forward in order to restore 

 the equilibrium. In doing this, the first foot to quit the ground will usually 



