THE FRAMEWORK OF THE HORSE. 43 



leg is stretched out towards P, and the angles become 

 natter. It is therefore evident that, both in a state of 

 rest and of action, the fourteenth vertebra is constantly 

 the centre of motion; and it is precisely from our 

 practical knowledge of this beautiful mechanism that 

 judges of horses attach so much importance to the 

 length of these two levers, and to their lying at right 

 angles to the hip-bone and shoulder-blade respectively 

 which is recognised by the form of the haunch, and 

 what we call a good shoulder ; the length of the stride 

 and its power depending, as is very evident, on those 

 particulars to a great extent. 



A farther proof of the same fact may be gathered 

 from Plate II., which shows the principle muscles, and 

 the way in which they are arranged. It is those in 

 the back, loins, hips, and shoulders, that concern us 

 here more especially; and we perceive that the princi- 

 pal ones of these all coalesce, as it were, into the large 

 flat tendon covering the identical portion of the back 

 pointed out as the centre of motion. This tendon, like 

 all others, is devoid of contractile power; and the cor- 

 responding sets of muscles of the fore and back hand 

 exert their contractile powers upon it in opposite direc- 

 tions, whilst it remains stationary, so to say the whole 

 process having a certain analogy with the familiar in- 

 stance of a pair of curtains drawn forward by cords to 

 the middle of a window. 



According to the laws of mechanics, when two forces 

 of equal intensity cross each other, as the lines P Q, 

 R S, do in fig. 4, the line in which the combined re- 

 sult of both is further propagated will lie equally dis- 

 tant from and between the two original forces and this 

 is, in the instance before us, perpendicularly upwards, as 



