Course
It perforates the lateral head of the triceps brachii muscle at the triceps' attachment to the humerus.
The upper and smaller branch of the nerve passes to the front of the elbow, lying close to the cephalic vein, and supplies the skin of the lower half of the arm.
The lower branch pierces the deep fascia below the insertion of the Deltoideus, and descends along the lateral side of the arm and elbow, and then along the back of the forearm to the wrist, supplying the skin in its course, and joining, near its termination, with the dorsal branch of the lateral antibrachial cutaneous nerve.
Read more about this topic: Posterior Cutaneous Nerve Of Forearm