Galen's Typology of Organs.

This paper examines Galen's insistence that the stomach and heart, despite their anatomical and physiological similarities to muscles, are not muscles. Through analyzing key passages in Galen's works, we show that this claim is rooted in a consistent tripartite distinction between organs: Psychic Moving Organs (muscles), Natural Moving Organs (e.g. stomach, heart), and Natural Immobile Organs (e.g. liver, kidneys). We argue that this classification is grounded in anatomical differences between flesh and fiber that Galen deems salient enough to support further physiological explanations and corroborate his philosophical-psychological commitments. By tracing the empirical foundations and theoretical motivations for these distinctions, we shed light on the relationship between Galen's anatomical practices and his physiology and psychology.