This plexus is formed by the union of the four lower cervical and first dorsal nerves. It extends from the lower part of the neck to the upper part of the axillary space, and terminates opposite to the coracoid process of the scapula in three cords— outer, inner, posterior— which supply nerves to the upper limb.

The branches of the brachial plexus are divided into those which are given off at the root of the neck above the clavicle, and those given off in the axilla below the clavicle. A connection is established between the cervical and brachial plexuses by the descending branch of the fourth nerve uniting with the fifth nerve.