— But in that case, perhaps there should be four separate receptacles of four sections each. It is, therefore written (Shemoth 13:9) "and as a remembrance between your eyes" — one receptacle for four totafoth.
(Devarim, Ibid.) "upon your hand" — the height of the hand (i.e., the upper arm). You say "the height of the hand" is meant. But perhaps "your hand," literally, is intended. It follows, since Scripture prescribes tefillin for both hand and head, that just as the head tefillin are on the height of the head, so, hand tefillin are on the height of the hand (i.e., the upper arm).