282 THE EXTERIOR OF THE HORSE. 



the foot is on the soil in such a manner that, at its termination, when 

 the foot is elevated, the tibia and the metatarsus are in a straight line. 

 It is apparent from this that the anterior canon, in this action, is espe- 

 cially utilized as an organ of support, whilst the posterior becomes a 

 veritable agent of impulsion. 



This region, however, only fulfils a passive role in locomotion. It 

 is an inert lever having no influence in itself upon the movements 

 which follow or precede it, since it is traversed in its length only by 

 tendinous cords, organs of transmission, and not by contractile muscles. 

 It is the same during station : its vertical direction and its inertia 

 make it a veritable column of support for the weight of the body, 

 whose total pressure accumulates upon it. It is therefore very appro- 

 priately disposed to fulfil this end. Besides being vertical, it also has 

 an almost cylindrical form ; its median bone has parietes of great 

 thickness ; the tissue which constitutes it is extremely compact ; finally, 

 by the concurrence of the rudimentary bones attached to its lateral 

 faces, it augments the area of the superior articular surface and serves 

 as an important apparatus of breaking concussion in virtue of the 

 double articulation which is found there and the obscure movements 

 which are produced there. 



Its tendinous cords, even, and the posterior ligament, from their 

 peculiar relations, present a special disposition to serve with .efficacy as 

 an apparatus of support. The carpal or tarsal check tendon relieves 

 the former by displacing a large share of the weight upon the bones, 

 while the obscurely muscular nature and the mode of intercrossing 

 of the fibres of the suspensory ligament of the fetlock 1 make this lig- 

 ament a veritable elastic brace, which disperses the effects of the weight 

 in such a measure as to render them compatible with the resistance and 

 integrity of the tissues. 



Finally, the action of the canon in relation to the impulsion is not 

 the same in the two members. This function, as we have seen, is more 

 particularly imparted by the posterior members. The extensor mus- 

 cles of the metatarsus are also provided with more powerful lever- 

 arms. The calcaneus, by its length and by the prominence which it 

 forms above and behind the centre of the tibio-tarsal articulation, 

 places these muscles in very favorable conditions relative to the inten- 

 sity of force and the rapidity of speed. 



1 From the point of view of comparative anatomy, the suspensory ligament of the fetlock 

 is, in fact, only a modified muscle which has its full development in the species whose hand and 

 foot approach, by the number of their digits, the conformation which is observed in man. Thus, 

 it occurs in quadrumana, carnivora, rodents, and many of the insectivora. 



