DISSECTION OP THE ANTERIOR LIMB. 13 



of blood which exudes from the smaller cut branches, it will contribute 

 to the neatness and cleanness of the dissection if the dissector will 

 carefully remove the vein and all its branches before he proceeds to 

 follow the nerves. 



The Brachial Plexus. The mode of formation of the plexus has 

 already been explained, and the student will recollect that he has 

 already followed branches from it to the levator anguli scapulse, 

 serratus magnus, and pectoral muscles, as well as the subcutaneous 

 thoracic nerve, and the filament furnished by the plexus to the phrenic 

 nerve. He can now easily identify and trace the following branches : — 



The Nerve to the Latissimus Dorsi (Plate 5) derives its fibres from 

 the 8th cervical and the dorsal roots of the plexus. 



The Nerve to the Teres Major (Plate 5) — one or more filaments, 

 generally deriving fibres, in common with the circumflex nerve, from 

 the 7th and 8th cervical roots (with possibly some fibres from the 6th). 



The Nerve to the Subscapularis (Plate 5) derives its fibres from all 

 the cervical roots of the plexus. 



The Circumflex Nerve (Plates 5 and 6). Its fibres come from the 

 7th and 8th cervical roots, and possibly also from the 6th. It turns 

 round behind the shoulder-joint in company with the posterior circum- 

 flex artery; and on the outside of the joint it supplies branches to the 

 teres minor, deltoid, mastoido-humeralis, and skin (Plate 7). It gives 

 a twig to the small scapulo-humeral muscle. 



The Suprascapular Nerve (Plate 5), deriving its fibres from the 

 6th, 7th, and 8th cervical roots, passes into the interstice between the 

 subscapularis and the supraspinatus. It then turns round the anterior 

 border of the scapula ; and, gaining its dorsal surface, is expended in 

 the supraspinatus and subspinatus muscles (Plate 8). 



The Musculo-spiral Nerve (or radial nerve) (Plates 5 and 6) is, at 

 its origin, the thickest of the nerves of the brachial plexus. Deriving 

 its fibres from the 7th and 8th cervical, and from the dorsal roots of 

 the plexus, it passes downwards and backwards on the subscapularis 

 and teres major muscles, and some little distance behind the axillary 

 vessels, from which it is separated by the ulnar nerve. On reaching 

 the deep humeral artery it disappears in front of the large head of the 

 triceps, and is continued round the humerus in the musculo-spiral 

 groove, where it rests on the brachialis anticus (humeralis externus), 

 and, afterwards, at the posterior or outer border of that muscle. It 

 reaches the front of the elbow-joint, being here deeply placed between 

 the brachialis anticus inwardly, and the origin of the great extensor of 

 the metacarpus outwardly. Before the nerve disappears behind the 

 humerus it gives branches to the great and small heads of the triceps, 

 and a long branch which passes backward to divide under the scapulo- 

 ulnaris for the supply of that muscle. Behind the limb it supplies the 



