Moses' arms grow heavy as he prays for the victory of the Israelites over the Amalecites; an outstretched arm is anatomically depicted. Etching by C. Sperling-Heckel, c. 1735.

The seventeenth chapter of Exodus tells us how Moses had to sustain a position of prayer with outstretched hands for as long as the battle with the Amalekites lasted in order to gain victory; after a while he needed assistance from Aaron and Hur, as depicted here. The relevant text of 'Physique sacrée' explains physiologically the stress Moses put on his arms, with the aid of the diagram of an arm at the top of the frame, labelled A to E. It explains how the muscles would tire and the blood would cease to circulate. It then points out the anatomy of the arm: "l'infraspinctus ou le sous-épinaux A le supraspinctus ou le sus-épinaux B le Deltoïde C le Biceps D le Brachial interne E & le Coracobrachial" (p. 116)