ward the center of the manege with croup toward the wall.
To obtain the shoulder-in, from left to right, the rider, having his mount in hand and forward, increases the pull of the left rein to flex the head and neck slightly to the left. At the same time, he increases also the effect of his left leg, carrying it a little backward on the flank, and thus pushes the haunches toward the right. Meanwhile, the right rein prevents the complete flexion of the neck to the left, and forces the left shoulder toward the right in front of the right leg.
The result is that the horse's left front leg passes in front of and across the right, while at the same time the left hind leg also passes in front of and across its mate. Thereupon, the horse, in order not to fall, steps out to the right with both right legs, and the first step of the shoulder-in is completed. Continuing the same effects continues the movement.
But the student, who considers anatomically the mechanism of the horse and its action in the various movements, will agree with the anatomist that the muscles and articulations of the horse's shoulder are not designed to allow natural movements of the humerus and scapula in any direction except forward and back. The horse, in short, is not a crab, built to go sidewise. The shoulder-in and the half-passage are therefore unnatural contortions compelled by riders who know no better.