THE AMERICAN TROTTING HORSE. 497 



do modify the manifestation of that power upon which speed does 

 depend. 



Let us now consider the essential element of speed at any -ait 

 whether it be running, pacing, or trotting. All the movement is 

 effected by the contraction of those masses of lean meat called 

 muscles. The muscles of voluntary motion are each attached to 

 two bones by its two extremities, and the bones being attached to 

 each other by a movable joint, when the muscle contracts one or 

 both of the bones must move; and, of course the rapidity of the 

 movement depends on the rapidity of the contraction. An animal 

 wills the movement of a limb; that will, which originates in the 

 brain, is transmitted through nerves to the muscles; they contract 

 and the limb moves. It would seem, then, that if a horse desired 

 to go fast, and his muscles were large enough and his joints supple, 

 he must needs do so whenever he tries ; for if the muscles obey 

 the will, and the will is that they shall contract quickly, the whole 

 thing would be accomplished. Speed would then depend on the 

 size of the muscles, and the willingness of the horse to contract 

 them rapidly. But the facts are clearly against such a theory ; for 

 all have noticed that a highly spirited horse that is very strong to 

 pull a load, may not be able to go fast in any gait. 



The truth is, that all power to move, lies not in the brain which 

 is the seat of the will, nor in the muscles which are the place of 

 the movement, but between the two, in the spinal cord, which 

 is the centre of the nervous system, and the generator of the 

 power. The spinal cord lies in the back bone, filling the carial 

 or hole that extends through its whole length, and giving off nerves 

 from every part of it that go to all parts of the body. It is con- 

 nected to the brain, and appears like a prolongation of it from the 

 cavity of the skull along the cavity of the spine ; but the rational 

 view of the spinal cord, and the one that is sustained by compara- 

 tive anatomy, is that which considers it the centre of the nervous 

 system ; the brain being an extension of it in one direction, and 

 the nerves an extension of it in another direction, the whole con- 

 stituting the nervous system. 



The brain is the seat of all mental manifestations of thought, 

 memory, love, fear, emulation, courage, &c. The disposition and 

 character depend upon the brain, but it is not necessary to animal 

 life. The -nerves extend to every part of the body; some of them 

 convey sensations to the brain, as of heat, or cold, or pain ; others 

 of them go to the muscles, and convey to them the power that is 

 generated in the spinal cord by which they contract. The will 

 to move is conceived in the brain, and goes to the spinal cord, 

 which then generates the power to move. The power, which for 

 convenience of language we will call nerve force, is sent through 

 the nerves and expended in the muscles, effecting their contraction 

 2* 2 1 



