206 



THE EXTERIOR OF THE HORSE. 



Let us suppose now that the extensors of CD and those of C^D'' are 

 shortened through the same space {CE^ C'F), a phenomenon which, however, in 



reality does not occur, since 

 the muscles are of differ- 

 ent lengths. The arm CD 

 will be carried to £"(?, while 

 C^D^ will be displaced to 

 FH. Whence it follows 

 that the point D will reach 

 a situation more advanced, 

 O, in relation with the 

 limit of extension, than the 

 point D'', which will de- 

 scribe the arc 7)^7/ always 

 smaller than the arc DO 

 under the special proposi- 

 tion with which we started 

 /AC IT AC'^ 



\ad ^^"^"^"S AD^ 



Fig. 58. 



yj 



The angular dis- 

 placement of the short 

 arm, CD, is therefore 

 more extensive for an 

 equal contraction or 

 shortening of the mus- 

 cles than that of the 

 long arm, CD'. 



In addition, the ex- 

 tensors of the shoulder 

 AB are longer than 

 those of the shoulder 

 AB'. Consequently, the 

 muscles of the latter are obliged to shorten themselves more for the 

 production of the displacement DG, which the extensors of AB will 

 effect without fatigue. 



Finally, as the effort of a muscle varies according to certain condi- 

 tions, among others with the resistance to be displaced, it follows that 

 the shoulder AB will produce the extension of the arm CD more 

 easily than AB' that of the arm CD', since the former is shorter and 

 consequently less heavy than the latter. 



Thus the length of the shoulder in comparison with that of the 

 arm shf)uld be as great as possible, for the reason that it effects a 

 greater displacement of the humerus with a more feeble muscular con- 

 traction. 



