MOVEMENTS UPON PLACE. 469 



good spirits, of impatience to act, or of restiveness ; to defend himself, 

 attack, leap, or, finally, to mount the mare. 



Its accomplishment is preceded by a very short preparation, during 

 which the members are drawn together and the head quickly lowered, 

 often several times repeated. Then the time of execution is manifested 

 by the sudden and successive extension of the head, the neck, and the 

 trunk, and, finally, by the energetic contraction of the extensor muscles 

 of the fore-limbs, which are at first semi-flexed. The extensors of the 

 head, of the spine, and of the anterior members, the gluteal and the 

 ischio-tibial muscles, are the principal agents in this sort of rotation of 

 the fore-quarters upon the hind-quarters. 



As soon as rearing is effected, the foothold exists only on the pos- 

 terior bipeds, whose segments, more or less flexed, are maintained in 

 situation by the contraction of their extensors. We can thus see the 

 amount of the resistance which the animal must overcome and the 

 length of the lever upon which it acts ; we can also easily understand 

 the readiness with which the line of gravitation tends to fall outside of 

 so narrow a base of support. All this explains the shortness of the 

 duration of rearing. Soon after it is accomplished, the fore-part of 

 the body is lowered and the fore-feet fall upon the ground. 



Nevertheless, there are some very vigorous horses capable of main- 

 taining this attitude for a much longer time than others. This is true 

 on condition, as Borelli l says, that tfye base of support be frequently 

 displaced. H. Bouley 2 adds, that it is due to another fact, that their 

 hocks are wide, their lumbar, croupal, and ischio-tibial muscles well 

 developed, and that the fore-part of the body may be relatively light. 

 Those which are weak in the hock and in the loins only accomplish it 

 by the energy of their will ; but no sooner have they raised themselves 

 upon their hind-limbs than they will recover the quadrupedal station 

 or else fall over sideways or backward. The easy, natural rearing is, 

 therefore, a sign of force and of energy. The English hunter and the 

 Arabian horse execute it with great ease ; if these animals had not this 

 aptitude they would be incapable of launching themselves into space 

 with the marvellous agility which is peculiar to them, and could not clear 

 with so much ease the obstacles which they meet in the steeple-chases. 



The facts mentioned above are not very rarely observed ; the fol- 

 lowing are some examples : 



A stallion, called Le Commode, some twenty years of age, and placed 



1 Borelli, De motu animalium, 1734. (See Proposition CLXVIL, Tab. 13, Fig. 11). 



2 H. Bouley, Nouveau Dictionnaire de m6decine, de chirurgie et d'hygiene vt6rinaires, 

 t. ii. p. 655. 



