THE MEMBERS. 



193 



FIG. 53. 



Let us suppose the two segments OC and OC / to have different obliquities 

 when compared with the vertical line OX (Fig. 53). 



Let, on the other hand, COB' be the maximum extension of the angle COB. 



The angles, in extension, being 

 equal, for anatomical reasons, to the 

 segment OC', the limit of extension 

 of OB will be B". A simple in- 

 spection, however, shows that OB", 

 being less inclined upon OX than 

 OB', will also be less favorably di- 

 rected than OB' in relation with the 

 vertical line OX. Therefore, the 

 orientation 01), bisecting the angle 

 COB, is more favorable than the 

 orientation OD' bisecting the angle 

 C'OB. 



It can only be alleged that the 

 angle C'OB, since it is more open 

 while the horse is standing still, 

 should be the same in action, but if 

 it were thus the conditions would no 

 more be equal, and consequently no 

 more comparable. The condition of 



the maximum opening of the angle C'OB changing, it can be assumed that in 

 the same manner the angle COB is caused to vary. Moreover, anatomy teaches 

 that there exists for these two angles a maximum separation, practically the 

 same, but dependent upon the disposition of the articular surfaces and the liga- 

 ments limiting their displacement. The sole difference which distinguishes them 

 is that in repose their branches are unequally inclined. 



Mode of Evolution of the Members during Progression. 

 The mode of evolution or oscillation of the members during progression 

 involves quite a complex analysis, but we must be able to explain its 

 general features in order to understand some subsequent phenomena. 



Let us examine this oscillation in the walk, a mode of progress in 

 which the body is never entirely disconnected from the ground. 



The foot, now elevated from the ground and now in contact with 

 it, passes through two principal phases : one of elevation, 1 during 

 which it is in the air, and one of contact, during which it supports 

 a portion of the weight of the body. During this evolution, the line 

 of direction of the member appears to oscillate alternately around 

 two points situated at its superior and its inferior extremities ; the foot, 

 the inferior extremity, is the point of the phase of contact ; the supe- 

 rior, the centre of movement of the shoulder or the croup, is that of 



1 The reader must have a clear conception of the meaning of the terms elevation and contact, 

 because they are frequently employed in the following chapters. 



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