M. cervico-humeralis--a case report.

An abnormal muscle, so-called M. cervico-humeralis, was found bilaterally in a 50-year-old Japanese male in a dissection practice at Jikei University in 1989. This is the third report of the cervico-humeral muscle in Japan, and the first case which occurred bilaterally. Both muscles were similar in shape, origin, course, and insertion. The flat and triangular-shaped muscle arose by tendinous slips from the transverse processes of the sixth and seventh cervical vertebrae (VC6 and VC7). These two tendons converged to form a single slip which passed through the brachial plexus. This single slip became a muscle running obliquely downward and laterally together with the brachial plexus and subclavian vessels to reach the medial surface of the humerus. The muscle inserted linearly by a thin flattened tendon into the lower end of the lesser tubercle and into the medial lip of the intertubercular sulcus of the humerus. The supplying nerve originated directly from the posterior cord of the brachial plexus in both muscles. The artery to the right cervico-humeral muscle arose from the axillary artery together with a branch to the subscapular muscle.