The mixing or joining together of nerves to form plexuses is one of the methods which nature adopts in order to establish a material relation of distant parts, and to some extent a dependency of one part upon another, so that the whole shall be capable of co-ordinating and acting simultaneously and together. The brachial plexus is a large fasciculus or bundle of nerves resulting from the combination of the inferior divisions of the last three cervical and first two dorsal roots. It is chiefly intended for the supply of the fore-limb with the nerves which animate it.

The branches going to make up the brachial plexus converge together after leaving the spine, the dorsal division winding round the front of the first rib and joining the cervical portion to form a broad flat band which passes between the superior and inferior heads of the scalenus-muscle, and subsequently breaks up into the following branches: -

1. The Diaphragmatic.

2. The Suprascapular Nerve.

3. Nerves to the Pectoral Muscles.