Anatomy of branches of the musculocutaneous nerve to the biceps and brachialis in human fetuses.

Forty upper limbs (20 right and 20 left) of spontaneously aborted human fetuses were examined to determine the branching patterns of the musculocutaneous nerve. The mean age of the fetuses was 21.3 weeks. We identified three branching patterns of the musculocutaneous nerve to the biceps muscle. Type I with a single primary branch occurred in 47.5% of cases. Type II with two primary branches each to a separate head of the biceps muscle was observed in 42.5% of cases. Type III consisted of two primary branches, the proximal dividing into two branches, each to a different head of the biceps, and the distal branch supplying the common belly. Type III was present in 10% of cases. We found only one branching pattern for the brachialis muscle, a single primary branch. In our material communicating branches between the median and musculocutaneous nerves were found in 20% of specimens. We measured the distances between the acromion and the exit points of the first and second branch to the biceps, which averaged 36.3% for the first branch regardless of the type of branching pattern, 54.2% for the second branch in Type II, 60.7% for the second branch in Type III and 60.9% for the branch to brachialis, expressed as a percentage of the distance between the acromion and the lateral epicondyle.