[Does the thumb have two phalanges or three? Development of ideas since Aristotle]

Many controversies mark the long road of the history of anatomy. The hand is not exempt of them. Even Galen's clear thinking, founded on the strict determinism between the structure of an organ and its function, and based on animal dissection, was criticized. In view of the structural complexity of the hand, we will limit our study to one of the most symptomatic conceptual disagreements: whether the human thumb has two or three phalanges, according to whether we include the first metacarpus, or if the thumb's first phalanx is considered as the initial element. According to the latter theory, there is a missing element in the first digital row, and this missing element is the metacarpus. This theory is ancient and its evolution throughout history is discussed in our study. Finally, we explain the origin and bases of the reasoning that led us to suggest the word 'metaphalanx' to designate the first metacarpus.