Hilton's law

Hilton's law is the observation that in the study of anatomy, one often finds that a nerve that innervates a joint also tends to innervate the muscles that move the joint and the skin that covers the attachments of those muscles.

For example, the musculocutaneous nerve supplies the elbow joint of humans with pain and proprioception fibres. It also supplies biceps brachii, brachialis, and the forearm skin close to the insertion of each of those muscles.

Hilton's law arises as a result of the embryological development of humans (or indeed other animals).

Extensions of the law
Hilton's law is described above. Similar observations can be made, to extend the theory; often a nerve will supply both the muscles and skin relating to a particular joint. The observation often holds true in reverse - that is to say, a nerve that supplies skin or a muscle will often supply the applicable joint.