6o 



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 Vertebra; — 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 observations which 

 are given here, are necessary for an explanation of the movements 

 of the horse in his various paces ; but others, in order that the\^ 

 may be understood, have been kept back, until the nature of the 

 paces and the mechanism of draught have been discussed. 



Displacement of the Centre of Gravity. — Locomotion is 

 effected by the 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. 25 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 (p) 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 (Fig. 26) ; it is 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 (Fig. 27). Precisely the same actions take 



