Coracobrachialis

What it is

A slender muscle running from the coracoid process of the scapula down to the middle of the inner humerus, lying deep in the armpit. Its name is simply its route: coracoid to brachium.

It shares its origin tendon with the short head of biceps brachii.

Its distinguishing feature is that the musculocutaneous nerve pierces straight through it on its way down the arm — one of the few muscles in the body a major nerve passes directly through, and a reliable landmark in dissection.

What it does

Flexes the shoulder — raises the arm forward — and adducts it, pulling it towards the body. It also contributes modestly to holding the head of the humerus in place.

It crosses only the shoulder, so unlike the biceps it does nothing at the elbow.

What loads it

Shoulder flexion and adduction against resistance, alongside pectoralis major and anterior deltoid, which are far larger and do most of the work.

What is commonly got wrong about it

That it can be trained. Every action it performs is performed far more strongly by a larger neighbour. There is no exercise that targets it, and no way to tell whether you have.

That it is part of the biceps. It shares an origin tendon and nothing else — different insertion, different joints crossed, different job.