BACK, Back-Bone, or SPINE. See Anatomy, n° 30. BACK, in the manège, and among farriers. A horse's back should be straight, not hollow, which is called saddle-backed: horses of this kind are generally light, and carry their heads high, but want in strength and service. A horse with a weak back is apt to stumble.
In the French riding-schools, to mount a horse a dos, is to mount him bare-backed without a saddle.