The early Stoics do not seem to have physiological theories about the workings of the human body. This is not surprising in light of Chrysippus' admission, reported by Galen, of his ignorance of anatomy. Yet a physiological theory explaining the mechanics of how the body moves in response to the soul's desires can be reconstructed from a handful of neglected fragments. Interestingly, the revealed theory is nearly identical to Aristotle's explanation in On the Motion of Animals of "how the soul moves the body in voluntary motion" (700bl0 and 703b3). In this paper I reconstruct the Stoic theory, and argue that it is most likely adopted directly from Aristotle.
Sakezles, Priscilla, "Aristotle and Chrysippus on the Physiology of Human Action" (1996). The Society for Ancient Greek Philosophy Newsletter. 454.