THE MEMBERS. 189 



during the beginning of the effort of traction, they can only support 

 that portion of the body and take a position to prepare themselves for 

 the effort which they are to execute the following instant. Besides, 

 this phase is of a very short 

 duration, and the backward 

 obliquity soon manifests it- 

 self. The latter exists al- 

 ready at the end of a certain 

 period when the canon is 

 still inclined forward. The 

 phase cannot be expected in 

 the draught-horse, as we 

 shall clearly see if we reflect 

 upon the fact that the body 

 of the animal is continu- 

 ally inclined forward during FIG. 51. 

 the efforts of traction. In- 

 stantaneous photographs place this matter beyond a doubt (Fig. 51). 1 



Mechanism of Impulsion. Whichever of the members we 

 examine, the impulsive force which they develop at a certain period 

 in their acting as a support results invariably from a more or less forci- 

 ble extension of the bony segments at the moment when the members 

 are supported against the trunk or the collar. It is an interesting and 

 important fact that we can prove scientifically that this process of exten- 

 sion is the conjoint function of most of the muscles belonging to the 

 limb which originates the impulse. Many of the flexors are capable of 

 contributing to this end, either because they cross over several articular 

 angles and attach to the convex side of one of them, 2 or because they 

 originate from the trunk and concur to straighten the inclined levers upon 

 which they terminate. 3 As to the abductors and adductors, they can, 

 by acting simultaneously, perform the role of extensors. The other mus- 

 cles maintain the osseous levers in their proper plane as compared with 

 the median plane of the body, and prevent their outward or inward dis- 

 placement after the manner of the ropes which fix the mast of a ship. 



1 See, for further details and interesting discussions by modern authors, H. Bouley, Nouveau 

 dictionnaire de me'deeine, de chirurgie et d'hygiene vtrinaires, tome i., art. " Allures," p. 360, 

 Paris. 1856; G. Colin, Physiologic comparee des animaux, t, i., p, 448, 3e ed., Paris, 1886; G. 

 Neumann, Du tirage du cheval, in Rec. de mm. et observ. sur 1'hyg. et la m6d. 6t. milit., anne 

 1876; ibid., Sur les elements de rimpulsion, in Revue v6te>inaire, annee 1886, p. 528; G. Chenier, 

 contribution a 1'etude des actes locomoteurs, in Echo des soc. et assoc vtfir., Juin, 1866. 



2 Such are : the flexors of the metacarpus, of the phalanges, of the forearm, of the metatarsus, 

 the ischio t'bial muscle 5 :, etc. 



8 Such are : the psoas, the superficial gluteus. the great dorsal, etc. 



