218 



THE EXTERIOR OF THE HORSE. 



FIG. 65. 



influence on the value of the scapulo-humeral angle, it may be asked 

 if, for velocity or speed, a straight shoulder will not in a measure be 

 compensated by an excess of obliquity of the arm. In other words, is 

 it rational to prefer (Fig. 65) an angle AOB to an angle COD, both 



having the same dimension? Evi- 

 dently it is : to a straight arm an 

 oblique shoulder; this is the law, 

 and for several reasons already known. 

 We will recall them : An oblique 

 shoulder will augment the elevation 

 and extension of its point, from the 

 same quantity of muscular contrac- 

 tion ; whence it follows that the in- 

 ferior extremity of the member will 

 be carried more in advance of its 

 primitive position. As the straight- 

 ening of the humerus also tends to 

 the same result, the two acting in uni- 

 son will increase the total amplitude 

 of the movement. 

 If, on the contrary, the conditions be the reverse, if the arm be 

 very oblique and the shoulder straight, the scapulo-humeral angle, 

 although equal to the preceding, will be restrained to a less separation 

 of its branches, because the extremity of the shoulder and the humero- 

 radial articulation will remain too far backward in order to give to the 

 forearm and the canon the ease and the time to be carried sufficiently 

 far in advance. 



To recapitulate, the inclination of the humerus should not be exces- 

 sive in rapid motors, and the conditions of a good orientation of the 

 scapulo-humeral angle must be found in the obliquity of the shoulder. 

 This explains why certain subjects, well marked in appearance in 

 relation with their articular angles, do not confirm the conclusions 

 which are based upon them. It suffices not (as we have seen on page 

 191) that the angles may have freedom of action, but it is also neces- 

 sary that this action may be effected in the direction of the movement. 

 If their orientation in relation with the vertical line of the centre of 

 movement is defective, all the mechanical advantages for the accom- 

 plishment of our aim, speed, are lost. 



These considerations, upon which we have purposely insisted, are 

 not applicable to services which only exact strength. We will except,, 

 however, the rapid draught-horse, in which the elements of force seem 



