This section is from the book "Hints To Purchasers Of Horses", by Charles Knight. Also available from Amazon: Hints to Purchasers of Horses.
A horse, in his walk, should begin by stepping boldly away, with his knees well bent, and his foot up, and placed down again flat; the feet if any thing first; with his hind legs tucked close, and following his fore legs regularly: he should not go with a hind and fore leg of the same side at a time, (which pace is termed ambling,) but in exact, and well-timed motion.
The same is to be observed in his trot; the knee should be bent, and the foot up, and sent straight fore-ward, not dishing on either side. The motion should be from the elbow, as well as the knee, for horses that step from the knee alone, soon tire themselves, and are always slow, putting the foot down nearly in the same place whence taken up. The hocks also should be tucked close together, and go well under the animal, with the same regularity which I mentioned as requisite in the walk. The fore and hind legs should go together, and not at twice, as if the animal had a joint in its back.
Observe, in all good trotters, the the rider can see the knees at every step without leaning forward in his saddle.
 
Continue to: