3G4 THE ARM. 



THE ARM. 



The ^47-)??, extending from the elbow to the knee (see K and L, p. 140, 

 and also cut, p. 360), consists in the young horse of two distinct bones. 

 The long and front bone, called the radms, is nearly straight, receiving 

 into its upper end the lower head of the humerus ; and the lower end 

 corresponding with the upper layer of the bones of the knee. The short 

 and hinder bone is called the tdiia. It has a very long and powerful 

 projection, received between the heads of the humerus and called the 

 elbow ; it then stretches down, narrowing by degrees (see L, p. 140, and 

 the cut, p. 360) to below the middle of the front bone, where it terminates 

 in a point. The two bones are united together by cartilage and ligament ; 

 but these are by degi'ees absorbed and changed to bone, and before the 

 horse becomes old the whole of the arm consists of one bone only. 



It will be perceived tha t, from the slanting direction of the humervis, 

 the weight of the horse, and the violence of the concussion, will be shared 

 between the radms and the uhia, and therefore less liable to injure either. 

 The circumstance, also, of so much weight and jar being communicated 

 to them, will account for the extensive and peculiarly strong union 

 between these bones in the young horse ; the speedy inflammation of 

 the uniting substance and absorption of it, and the substitution of bone, 

 and complete bony union between the radius and ulna, in the old horse. 

 The immense muscles that are attached to the point of the elbow likewise 

 render it necessai'y that the union between these bones should be very 

 strong. 



The arm is a most important part of the horse, as will be seen when 

 we describe the muscles which belong to it. The muscles proceeding from 

 the shoulder-blade and the humerus, and inserted into the elbow, are the 

 grand agents in extending the arm, and in proportion to the power which 

 they exert will be the quickness and the length of the stride. The strength 

 of the horse, so far as his fore-limbs are concerned, principally resides 

 here. Then there will naturally be a large and muscular arm, and such a 

 formation of the hmb, and particularly of the elbow, as will enable these 

 muscles to act with most advantage. 



The principle of the lever (referred to at p. 360) is here beautifully 

 applicable. The elbow-joint is the centre of motion ; the whole of the 

 lower part of the leg is the weight to be raised ; and the power by which 

 it is to be raised, in one act of progression — the extending of the Hmb, is 

 the muscles inserted into the elbow. In proportion as the weight is more 

 distant than the power from the centre of motion, as it is in the construc- 

 tion of this limb, so will be the greater degree of energy requisite to be 

 exerted. Supposing that the weight, taking the knee to be the centre of 

 it, is eighteen inches from the elbow joint — that the limb weighs 60 lbs., 

 and that the elbow projects two inches from the joint — then an energy 

 equal to nine times the weight, or 540 lbs., will be needed to move and 

 extend the hmb, because the weight is nine times farther from the centre 

 of motion than the power is. If in another horse the point of the elbow 

 projects three inches from the joint, the weight of the leg remaining the 

 same, only six times the force, or 360 lbs., will be required, making a 

 difference in, or saving of, muscular action, equal to 180 lbs. in each 

 extension of the arm. If a few pounds in the weight of the rider tell so 

 nmch for or against the horse in a long race, this saving of power must 

 make an almost incalculable difference ; and^ therefore, judges of the horse 

 rightly attach so much importance to the dejith of the elbow, or the pro- 

 jection of the point of the elbow from the joint. 



