ATTITUDES. 443 



in fact, exist upon the same vertical line (the angles not varying) only 

 on condition that the segments maintain certain determined lengths, or 

 that the angles (the segments remaining the same) have an equally 

 determined opening. 



But, as the variations of the two factors of which we have spoken 

 are always simultaneous and not independent, it follows that two horses 

 provided with good axes are not necessarily identical in relation to the 

 extent of the articular angles and the length of the bones, because 

 deviations in the one are properly compensated by contrary modifica- 

 tions of the other. 



a. Axes of the Anterior Members. 



Axes viewed in Profile. — It is particularly difficult to locate 

 the line of direction of the anterior member on account of the more or 

 less diffuse points of attachment of this member. What is, indeed, 

 the exact centre of the combined actions of the trapezius, the rhom- 

 boideus, the angularis, the great serratus, the pectorals, and the mas- 

 toido-humeralis, which fix the shoulder and the arm against the sides 

 of the thorax, and almost make them integral parts of the trunk? 

 While we know with sufficient precision the insertion of each of these 

 muscles, and while we are able to determine in an approximate manner 

 the directions in which they act, we are still ignorant of the vole which 

 each one plays in supporting the trunk. We are therefore obliged to 

 depend alone in this respect upon empirical data. 



Consequently, let us choose that horse which is recognized by uni- 

 versal practice as having beautiful axes (Fig. 147). Thus, as we have 

 said above, it is to be supposed that the inferior extremity of his fore- 

 members will be situated in the vertical line which passes through the 

 corresponding centre of movement of the body. Through the middle, 

 6, of the anterior foot let us draw this line. We will see that it meets 

 the scapular segment at a point, a, which is often located at the same 

 time with remarkable accuracy upon the horizontal line ae, which 

 passes precisely through the coxo-femoral articulation, the known centre 

 of movement of the posterior column upon the trunk. 



It is therefore probable that the centre of movement, a, of the shoulder, 

 whose situation otherwise varies according to the inclination of the latter, occu- 

 pies, in a beautiful conformation, a height equal to that of the centre of movement 

 of the haunch. 



If such really be the case, the plane of suspension of the body upon the 

 members will be a horizontal plane. We except, of course, those particular 

 cases in which the withers are low and the fore part of the trunk larger or smaller 

 than the hind part. We know that there is, in the latter cases, an irregular 



