The first illustration describes a disciplined horse that remains standing while its rider dismounts and places the reins over the front of the saddle. The pose of the reins and saddle is pictured through a seated human posture.
The image cannot be understood by focusing on a single rare noun: the locations of the saddle pommel, reins, and bit must be visualized together.
The horse’s training is the subject matter; the metaphor’s technical novelty lies in noticing the resemblance between the tack’s arrangement and the posture called iḥtibāʾ.