Morphological study, by teasing examination, of the communication from the musculocutaneous to median nerves.

Nine specimens with communications from the musculocutaneous to the median nerves were investigated, by teasing examination, from their origins in the brachial plexus to their final destinations in nerve fibers. The nerve fibers of the communications were derived from the sixth and seventh cervical ventral rami of the spinal nerves. The distributions of the nerve fibers of the communications were divided into four types. In Type A, the nerve fibers reached the thenar muscles and the lateral digital nerves. In Type B, they reached the pronator teres or flexor carpi radialis muscles in addition to Type A. In Type C, they reached the anterior interosseous nerve area in addition to Type B. Finally in Type D, they also reached the distal muscle belly of the index of the flexor digitorum superficialis. It was revealed that there was a definite rule in the distribution of the nerve fibers in the communications from the musculocutaneous to median nerves. The area of the distributions was expanded in order from the thenar muscles to the flexor muscles of the forearm. The results in this study are useful for proper diagnosis and treatment of the peripheral nerve injuries involving the musculocutaneous and median nerves.