An arm that sweeps in one line from the shoulder to the floor cannot be made from one piece of timber, and hiding that fact is the whole job.
The curve is too long and changes direction too much - somewhere along it the grain would have to run across the section, and that is where the arm would break the first time someone leaned on it heavily.
So the arm is built from three shaped pieces, jointed where the curve is momentarily straightening: once just below the shoulder scroll, once above the foot. Those are the two points where two consecutive pieces meet almost in line, which gives long glue faces and keeps the grain running along the curve everywhere it matters.
The carving is then set out across the assembled arm as one continuous design and cut afterward, so no ornament stops at a joint. On a natural-finished piece the joints are visible if you look for them, at the two places where they are structurally correct - and our artisans would rather you saw an honest joint in the right place than a hidden one in the wrong place.