The brachial plexus is a network of nerves, running from the spine, formed by the anterior rami of the lower four cervical nerves and first thoracic nerve (C5–C8, T1). The brachial plexus passes through the cervicoaxillary canal in the neck, over the first rib, and into the axilla (armpit region), where it innervates the upper limbs and some neck and shoulder muscles.