The difference between shoulder in and two-track work is analogous to that between haunches in and two-track work. In the movement of shoulder in, if the trooper eases the hands slightly, the horse, being bent and not obliqued, will quit the track and start to make a circle. If, in haunches out on two tracks, the trooper eases the hands, the horse, being traversed and not bent, quits the track and moves off at an oblique.
About on the haunches.—The about on the haunches consists in causing the forehand to describe a half circle around the haunches. It is a difficult movement and, customary methods of instruction to the contrary notwithstanding, should not be taken up until after the completion of the exercises of haunches in and shoulder in.
The first part of the movement is easy enough, but the last part is difficult. Take for instance the right about. Begin the movement like a change of direction to the right, holding the haunches firmly with the left leg. In the remainder of the exercise the controlling aids are the left rein and the left leg. The left rein has first a bearing effect that, assisted by the right rein, swings the forehand on its path; thereafter, it has an effect of diagonal traction, pulling the mass back upon the right hock and thus holding the haunches stationary.
The about on the haunches is executed on the inside hind leg, the outside hind leg gaining ground around it.
Lateral effect and diagonal effect.—The movements that have been already executed with the rein and the leg: on the same side suffice to show the difference between the lateral effect and the diagonal effect.
It is easy to see that the former is the means and that the latter is the end in view. With young horses the right rein comes to the assistance of the right leg—lateral effect. With trained horses the rein places or controls the forehand while the leg controls the haunches—diagonal effect.