Electro-physiology and electro-therapeutics : showing the best methods for the medical uses of electricity / By Alfred C. Garratt.

hence are the five spinal roots of the nerves of the arm and hand. We know, then, that the brachial or axillary plexus of nerves is formed by peculiar communications between the anterior branches of the four last cervical and first dorsal nerves; the fifth and sixth nerves unite to form a common trunk, which soon again divides into two branches ; the last or eighth cervical and the first dorsal likewise unite, and soon again divide into two branches ; the seventh cervical nerve passes outward between the two just described, and when opposite the clavicle it divides, and unites both with the one above and the one below, and so unites the whole; from which results the brachial plexus. This plex- us is broad and deep-seated in the neck, but narrows and becomes superficial as it descends into the axilla, and then again en- larges some at its lower part, where it divides into its six termi- nal branches. It lies under the two scaleni muscles, between which its nerves issue, and lower down it is found placed he- tween the clavicle and sub-clavius muscle above, and the first rib with the first serration of the serratus magnus muscle below. In the axilla this plexus is found situated by its outer border, resting against the tendon of the snb-scapularis muscle. At this point it completely surrounds the axillary artery by means of the two branches which are here sent off to form the nerve medianus. Now, so very important is it for us to be familiar with the ana- tomical relations of the nerves of the upper extremities, that we must patiently review all the more important branches in the hand, arm, and shoulder. Commencing, then, at the roots of the arm nerves, we find there five pairs of spinal nerves, the fifth, sixth, seventh, and eighth cervical and first dor- sal, whose anterior branches converge to form the great arm plexus. The posterior branches of the five pairs in question arc far less in size and importance than the anterior ; nevertheless, these small, short, and abrupt branches possess, here, no little interest for us. They at first set out merely vertically down- wards, and then turn inwards between the muscles of the hack, occupying the lower cervical and upper dorsal region, there throwing branches to the muscles as they pass, and then they