192 THE EXTERIOR OF THE HORSE. 



Unfortunately, these experiments have only determined the limited 

 positions in the walk, the trot, and the slow gallop, and leave us still 

 ignorant of what these positions are in extreme speed. Nevertheless, 

 from the facts already acquired, an important proposition can be 

 deduced : that the Inn it of extension of the locomotory segments occivpies, 

 in horses of speed, a point, A, quite close to a vertical line passing through 

 their centre of movement. 



According to the angles considered, this point is situated either in 

 advance of the vertical line mentioned (angles with the sine posterior), 

 or behind it (angles with the sine anterior). But it is apparent that the 

 farther the limit of extension passes beyond the vertical line of the 

 centre of movement the more will the angle of these segments, when 

 ;it is opened, be favorable to the augmentation of the obliquity of the 

 member, and consequently the more ^vill it tend to increase the ampli- 

 tude of the step or the extent of the movement. 



It would follow from this that the most favorable inclination of an 

 osseous lever is that which removes it the least from the vertical line 

 OX during flexion, and consequently that which tends to approach it 

 to this same line while the animal is standing still. In this case the 

 direction of the segment Mill be more closely related to the bisecting 

 line OC, which is associated, as we have seen, with the largest space 

 of oscillation. . 



In the preceding statements we have viewed an isolated locomotory 

 segment, as it is moved freely under the horizontal line MN, without 

 the intervention of foreign influences. This has permitted us to indi- 

 cate to the best advantage the direction of the segment associated with 

 a large and effective oscillation. 



In natural conditions, however, this arrangement is not so simple, 

 since the locomotory angles are formed by bones which are articulated in 

 twos or in threes. It is therefore in place to inquire whether, under these 

 circumstances, the extreme limits A and B remain always the same with 

 relation to the vertical line OX through the centre movement. 



It is easy to assure ourselves of the contrary. These positions de- 

 pend upon the inclination of the segment with which the one under con- 

 sideration is articulated. The maximum value of the articular angle 

 may be similar, and, for the sake of the argument, we may say equal ; 

 but the orientation of this angle being different, the extreme positions 

 A and B are displaced either forward or backward of the vertical line, 

 according to the obliquity of the adjacent segment. This will neces- 

 sarily result in differences in the utilization of the articular movements 

 in forward locomotion. 



