part of part of Homo sapiens proximal phalanx of manual digit 1 zone of long bone base of first proximal phalanx of hand 2026-03-19T00:00:00Z A zone of bone organ forming the proximal end of the proximal phalanx of the thumb, presenting an oval concave articular surface that receives the head of the first metacarpal at the metacarpophalangeal joint. David Osumi-Sutherland