( 57 ) 



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 

 Limbs — Action of the Muscles which extend the Vertebrae — Width between 

 each respective Pair of Legs as affecting Speed — Effect of Insecurity of Equili- 

 brium 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 under 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. lo 

 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 

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

 {sec Fig. 1 1) ; it will be evident that in order to prevent the body from 

 falling, 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 (see Fig. 12). 

 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 



