60 FORM AND ACTION. 



little bones whose use is to set the arms off from the shoulders — 

 the clavicles or collar-bones. 



The arm of the horse, the same as our own fore-arm — to which, 

 I repeat, it corresponds — has in its composition two bones, the ra- 

 dius and the \ilna ; but with this difference, that in man and the 

 monkey, and also in some quadrupeds, the ulna is a separate bone 

 of equal length with the radius ; whereas in the horse it is nothing 

 more than an attachment to the radius, the medium of union be- 

 tween them being in the young animal, and indeed up to the adult 

 period, an elastic (cartilago-ligamentous) substance, which yields to 

 force, and thus in action serves the purpose of a spring, diminishing 

 concussion. Indeed, this appears to have been one reason why the 

 ulna was not extended to the knee-joint : had it been a separate 

 bone no such spring could have existed. At full growth, however, 

 or very soon after, the uniting elastic matter becomes converted into 

 bone, consolidating the ulna with the radius, and for ever destroying 

 the original spring. 



At the superior part the ulna enters into the composition of the 

 elbow-joint, the same being the part which protuberates backward 

 and forms the elbow. Thus placed and fashioned, the ulna answers 

 two important uses : one is, extension of the surface of the joint 

 and limit to its motion backward, by serving as a stop to it; the 

 other is the leverage it offers for the insertion of muscles whose 

 office is to extend the fore-limb. The advantages derived from 

 long and prominent elbows are precisely such as are afforded by 

 length of lever in any situation out of the body : providing the 

 weight to be lifted and the lifting forces to remain the same, the 

 power of the latter will be increased in direct ratio with the length 

 of the lever — the elbow; and considering that the operation of 

 these muscles though immediately upon the arm, extends all the 

 way to the foot, a long lever may make a difference of some pounds 

 even in the capabilities of the fore-limb. So far as progression is 

 assisted by the fore extremities, it is by the action of the powerful 

 muscles inserted into the elbows : while the flexors of the arm 

 have only to lift the limb off the ground and advance it, the exten- 

 sor muscles — attached to the elbow — have, the moment the foot is 

 grounded, to aid in the grand operation of progression. We see, then, 

 the necessity for long and prominent elbows. Some horses appear 



