Musculocutaneous nerve pierces one of the following muscle:
The musculocutaneous nerve supplies the biceps brachi, brachialis & coracobrachialis.
It pierces the coracobrachialis, lies between the biceps & brachialis & continues laterally as the lateral  cutaneous nerve of the forearm.
It supplies the skin of forearm from the elbow to the wrist joint.
Morphology of the coracobrachialis: It represents the muscle of medial compartment of the forelimb of quadrupeds, In some animals, this muscle consists of three heads. In human beings, the upper two heads are fused and musculocutaneous nerve passes between the two fused heads. The lower third head has disappeared in humans. But, occasionally the lower head persists as a fibrous band (ligament of Struthers). The median nerve and brachial artery then pass deep to the ligament and may be compressed.
Corachobrachialis
Brachialis
Biceps
Brachioradialis