In order to understand the functions of teres minor, examining the compositions of teres minor muscle and the innervation of the muscle is very important. We used 20 shoulders from 10 cadavers in this study. We investigated the composition of the muscle bundles of teres minor and the innervation of this muscle. In addition, we examined four shoulders to investigate the insertions of the muscle bundles of teres minor muscle histologically. Teres minor muscle was composed of the upper part and the lower part. The upper part originated from the dorsal surfaces of the lateral edge of the scapula. The lower part originated from the fascia between teres minor muscle and infraspinatus muscle and the inferior surfaces of the lateral edge of the scapula. Two parts changed the positional relationship in the orgin and insertion. The upper part was situated inferiorly in the origin, however it was situated superiorly in the insertion. These two parts could not be separated from each other clearly. In the area of insertion, the upper part had a round-shaped attachment in the posterior surface of the greater tuberosity. On the other hand, the lower part had a line-shaped attachment in the surgical neck of the humerus. In cross-section of teres minor, its intramuscular tendon had two parts ; thick part superiorly, and thin part inferiorly. Teres minor was innervated by branches of the axillary nerve from the dorsal surface. The upper part and the lower part were innervated by independent branches of one nervous trunk to the muscle. According to the present findings of the innervations, the upper part and the lower part of teres minor muscle are almost totally independent from each other like two heads of the one muscle.
