32 Seats and Saddles, 



neck, which are much heavier than the tail at the other 

 extremity. 



Looking now at the spinal column, the framework of 

 the back, on which the rider's weight is to be placed, 

 we perceive that, whilst the under line of the vertebraB 

 is nearly straight, although not quite horizontal, inclin- 

 ing somewhat downward toward the forehand, the 

 spinal processes of the first thirteen vertebras of the 

 back (dorsal vertebrae), reckoning from the point where 

 the neck is attached, incline backward, whereas those 

 of the fifteenth, sixteenth, seventeenth and eighteenth 

 dorsal, and the six lumbar vertebrae, incline forward ; 

 the fourteenth dorsal vertebrae, with its process, stand- 

 ing perfectly upright, and forming, as it were, the key- 

 stone of the arch thus presented. It is very obvious 

 that this inclination of the processes toward a central 

 point is intended to and does limit the motion of the 

 back downward and upward (/'. ^., vertically), so that, 

 in fact, this fourteenth dorsal vertebra becomes the 

 ce7ttre of motion of the horse's body — the point about 

 which the several movements of the fore and hind legs 

 are performed with various degrees of rapidity, either 

 simultaneously or successively, and which constitute 

 the paces of the horse ; and this is further shown by 

 the distribution and points of attachment of the muscles 

 of the back and adjacent parts of the fore and hind 

 quarters. Putting, therefore, the progressive movement 

 of the animal out of the question as being equally ap- 

 plicable to all its parts, the internal motion of the seve- 

 ral parts of the body increases in proportion to their 

 distance from the fourteenth vertebra ; a7id the same is 

 applicable to burdens placed on the horse's back^ espe- 

 cially a rider ^ ^vhose frame is szibject to its own pecu- 

 liar motio7is^ some of which are caused by the progress- 

 ive 7noveme7it of the bearer. 



It has been already pointed out, that in consequence 



