A systematized computer technique of centroid analysis has been developed to evaluate the precise geometric relationship between a muscle and a bone and it has been applied to the abductor mechanism of the human hip joint. 2. The validity of the traditional use of straight lines for displaying the line of action of a muscle is open to serious question, although in the case of the gluteus medius the straight line simplification is not unmeasurable. 3. The determination of the precise interactions of muscles and bones is of major importance in the consideration of various orthopaedic procedures.
