SLANTING DIRECTION OF THE SHOULDER. 



257 



It must not perhaps be said, that the form of the spring was borrowed frvan thin 

 construction of the limbs of the horse, but the effect of the carriage-spring beautifully 

 illustrates the connexion of the different bones in the extremities of this quadruped. 



The obliquity or slanting direction of the shoulder effects other very useful pui- 

 poses. That the stride in the gallop, or the space passed over in the trot, may be 

 extensive, it is necessary that the fore part of the animal should be considerably ele- 

 vated. The shoulder, by means of the muscles which extend from it to the inferior 

 part of the limb, is the grand agent in effecting this. Had the bones of the shoulder 

 been placed more upright than we see them, they could not then have been of the 

 length which they now are, their connexion with the chest could not have been so 

 secure, and their movements upon each other would have been comparatively 

 restricted. The slightest inspection of the preceding cut, or of that at page 68, will 

 show that, just in proportion as the point of the shoulder is brought forward and ele- 

 vated, will be the forward action and elevation of the limb, or the space passed over 

 at every effort. 



The slanting shoulder accomplishes a most useful object. The muscles extending 

 from the shoulder-blade to the lower bone of the shoulder are the powers by which 

 motion is given to the whole of the limb. The extent and energy of that motion 

 depend much on the force exerted or the strength of the muscle ; but there are cir- 

 cumstances in the relative situations of the different bones which have far greatel 

 influence. 



Let it be supposed that, by means of a lever, some one is endeavouring to raise '. 

 certain weight. 



A is a lever, resting or turning on a pivot B ; C is the weight to be raised ; and D 

 is the power, or the situation at which the power is applied. If the strength ii 

 applied in a direction perpendicular to the lever, as represented by the line E, th 

 power which must be exerted can easily be calculated. 



A B 



In proportion as the distance of the power from the pivot or centre of motion 

 exceeds that of the weight from the same place, so will be the advantage gained. 

 The power here is twice as far from the centre as the weight is, and therefore advan 

 vantage is gained in the proportion of two to one : or if the weight is equal to 200lbs., 

 a force of lOOlbs. will balance it. If the direction in which the power is applied is 

 altered, and it is in that of the line F, will lOOlbs. effect the purpose 1 ? No; nothing 

 like it. How, then, is the necessary power to be calculated ? The line of direction 

 mast be prolonged, until another line, falling perpendicularly from the lever, and 

 commencing at the centre of motion, will cut it ; and the length of that line will give 

 the actual effect of the strength employed. Now, this new line is but half as long 

 as the distance of the weight from the centre o*" motion, and therefore advantage is 

 lost in the proportion of two to one ; or a strength equal to 4001bs. must be exerted 

 to raise the 2001bs., and so on in proportion to the deviation from the right or perpen- 

 dicular line. 



Let the shoulder of the horse be considered. The point of the shoulder the 

 shoulder joint is the pivot or centre of motion; the leg attached to the bone of the 

 arm is the weight; the shoulder-blade being more fixed is the part whence the power 

 emanates ; and the muscles extending from the one to the other are the lines in which 

 that power is exerted. These lines approach much more nearly to a perpendicular 

 in the oblique than in the upright shoulder (see cut). In the upright one, the shouJ- 

 tiei-blade ^nd the bone of the arm are almost in a straight line, and the real action 

 and powei 3f the muscle are most strangely diminished. In this point of view the 

 oblique shoulder is most important. It not only gives extensive action, but facility 

 of action. The power of the muscles is more than doubled by being everted in a 

 line approaching so much nearer to a perpendicular. 

 22* 2n 



