oakvile.
Intravenous feeding (into a vein) is still used today for balancing body fluids, particularly if there is vomiting and intense fluid loss due to diarrhoea.
You can insert the needle any where that a vein presents.arm, leg and even the scalp in babies.The big vein in the neck (Jugular or Subclavian) can also be used.
In you particular case, it might be that the only vein that they could find was on the inside of the ankle and even then, they may well have had to "cut down" at the ankle to find a vein.....1940´s you say.
Tubes can also be inserted into arteries, but this is hardly ever done for "feeding" purposes.