The homologies of the flexor and adductor muscles of the thigh

Abstract The literature relating to the flexor and adductor muscles of the thigh and their nerve supplies, in Sphenodon, the lizards, crocodiles and mammals was correlated and new dissections made of animals belonging to the last three groups. All of these muscles can be traced as individual entities from animal to animal without loss or addition to their number, although splitting may occur. The attachments of the muscles and their relationships to one another and to the two heads of the gastrocnemius are the same in all the reptiles studied. In the mammals one group, including the adductor longus and magnus and the retractor femoralis, has migrated from the tibia between the two heads of the gastrocnemius onto the femur, and another from the ilium onto the vertebrae, the one migration being caused by expansion of the gastrocnemius, and the other by expansion of the gluteal muscles. A new lateral flexor mass has been formed from part of the reptilian ilio tibialis by migration down the fibula. The nerve supplies of the various muscles are not constant when traced from group to group, and it is suggested that a muscle receives its nerve supply from the nerve nearest to it in embryonic development, so that when a muscle has migrated the nerve supply is no longer a reliable guide to its homology.