226 THE EXTERIOR OF THE HORSE. 



much more closed than when the bone in question is more vertical. In 

 order that the horse may have speed it is necessary that the forearm be 

 not only long but that it be also enabled to become flexed to a large 

 degree, so as to give the greatest possible amplitude to the step. The 

 more vertical the arm the better will this condition be fulfilled. 

 Such a disposition will, besides, favor the opening of the humero-radial 

 angle during the propulsion of the trunk, another qualification which 

 all the articular angles of rapid motors possess. Here observation con- 

 firms the theoretical data presented in discussing the arm. In race- 

 horses the latter region is not inclined, a disposition which, as we have 

 seen, is not incompatible with an extensive closing of the scapulo- 

 humeral angle, since the obliquity of the scapulum counteracts the 

 disadvantages which result from a vertical humerus. 



These slight variations in the direction of the bones and the mode 

 of opening of the superior articular angles of the members contribute 

 to explain the contradictory results which are observed in race-horses 

 of the best appearance as to conformation. Very difficult to appreci- 

 ate, these variations often pass unperceived and lead the observer into 

 error as to the importance of their effects. 



These, nevertheless, may sometimes be quite considerable, as we shall 

 presently see. 



Let us suppose, for an instant, that a horse be able, at each step, to open the 

 scapulo-humeral angle and close the humero-radial, each to a greater degree than 

 in another horse. Let us assume, also, to make use of round numbers, that this 

 feeble amplitude of two degrees is manifested upon a lever only one metre in 

 length. We know that the distance passed over by the extremity of this lever 

 for each degree will be : 



2irE 2 X 3.1416 



- 



This will signify that each step of this horse will be 34 millimetres longer 

 than that of the second horse. These 34 millimetres will give him an increase 

 of 22 metres and 644 millimetres over a distance of 4000 metres travelled at a 

 fast gallop (the step measuring 6 metres) ; at a fast trot (the step being 3 metres), 

 an increase of 68 metres. 



Thus, the influence of the articular angles merits to be taken into 

 consideration, in that they can determine the amount of speed which a 

 given animal is able to employ. As it has been well remarked, we 

 must take cognizance of only a very feeble augmentation for a very 

 short lever, as in the example which we have chosen. What might 

 have been the results if, instead of calculating them upon two degrees, 

 we had estimated them upon four, six, or eight, as it frequently 

 exists ? 



