PROGRESSION. 133 



that unless he gets his feet out of the line of march in proper time, 

 they must be trodden upon by the soldier behind, representing the 

 hind limbs ; so that, in point of reality, the quadruped, in his ordi- 

 nary movements, may be said to represent a double biped marching 

 out of step. 



With a view of rendering the order of movement of the four 

 limbs of the quadruped more intelligible, it has been common with 

 writers on the subject to note each foot by a letter or number : thus, 

 the fore legs are represented by the letters A, B, the hind by C, D : 

 supposing the A and C to denote the left or near legs, and B, D, 

 the right or off, fore and hind respectively, and that A moves first, 

 D will follow, and B will quit its place just in time for D to oc- 

 cupy it, while A will move off for a second time, just in time for 

 C, the last leg to move, to take the ground A stood upon ; up to 

 which period A has moved twice to C's once. Supposing a hind 

 leg, C, moved first, the fore leg, B, having to move next, A would 

 not quit its ground in time for C to occupy it. When it happens 

 that a hind leg does make the first step — as in horses or cattle 

 grazing or moving leisurely or heedlessly — the step proves to be 

 one short of the spot upon which the corresponding fore foot is 

 resting, and so the latter is saved from being trodden upon. In 

 this manner it happens that the fore and hind feet of the corre- 

 sponding sides become, instead of being in respect of one another 

 diagonally placed, approached close together on one side, standing 

 under the centre of gravity, while on the other side the fore is ad- 

 vanced, the hind being extended backwards. This is not a natural 

 position, but it is one that observably occurs in movements such as 

 I have been describing, and likewise in those that, through any 

 disturbance or derangement in action, are rendered irregular or 

 discordant — as, when in the gallop, the fore and hind legs of 

 opposite sides are in advance. So far as respects the common 

 paces of walking and trotting, this appears to be the analysis of 

 progression, the priority and order of motion of the animal's four 

 legs : acceleration of movement, so long as the same paces be 

 preserved, will not alter this order of succession, though it may 

 quicken it to that degree that time is not given for one foot to 

 reach the ground before the other is lifted off, and the conse- 



