Observations on the pollical palmar interosseous muscle (of Henle).

Questions about the existence of a "pollical" (first) volar interosseous muscle have persisted since its description by Henle in 1858. A survey of current human anatomy texts and atlases reveals that the majority do not recognize a pollical volar interosseous muscle and therefore they identify only three palmar interossei. We examined the thumbs of 20 individuals of African and European origin in the human anatomy lab at University of the Witwatersrand (Johannesburg) and 15 individuals of European ancestry in the anatomy lab at the University at Stony Brook (New York). A pollical palmar interosseous muscle (PPIM) was found in 86% of individuals (17/20 of the Witwatersrand sample; 13/15 of the Stony Brook sample). Here, we offer a definition of the PPIM in an attempt to resolve the long-standing question of its existence and its relationship to the adductor pollicis obliquus and the deep head of flexor pollicis brevis. We suggest that the human hand usually possesses four palmar interossei as well as four dorsal interossei.