The human gemelli muscles and their nerve supplies.

The superior and inferior gemellus muscles were examined as to their forms and the patterns of nerve supply in 13 human cadavers (20 specimens). The superior gemellus muscle (Gs) was absent in 3 specimens, but showed no accessory slip or fusion with the internal obturator muscle (Oi). The nerve to the Gs originated from the nerve to the Oi (OiN) in 7, the nerve to the quadratus femoris muscle (QfN) in 4, or both in 6 specimens. The inferior gemellus muscle (Gi) was present in all, but fused with the Oi in 3 specimens. In one specimen, an accessory muscle bundle was observed between the Gi and Oi. The Gi always received branches from the QfN at its anterior surface, but received an additional nerve supply at its posterior surface from the OiN or the pudendal nerve in one specimen each, and the accessory bundle was supplied by a branch from the OiN at its posterior surface. In a well preserved specimen, a branch to the Gi from the QfN entered the Oi and communicated with the OiN after supplying and leaving the Gi. The frequency of the dual innervation of Gs by the OiN and QfN was 29.3%, but that of the Gi and Oi could not be determined, because of the occurrence of the fused part, the accessory bundle and nerve communication. There existed some gross anatomical differences between both gemelli muscles; they are considered to be parts of the internal obturator muscle in a broad sense.