DISSECTION OF THE ANTERIOE LIMB. 13 



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 circumflex 

 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 SuPKASCAPDLAB 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 MnscULO-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 tlie 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 antious (humeralis externus), and, after- 

 wards, 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 medium head 

 of the triceps and the anconeus, and furnishes a few cutaneous branches 

 which perforate the caput medium, or emerge at its lower part, to be 

 distributed to the skin of the outer side of the fore-arm, below the 

 elbow. The termination of the nerve will afterwards be followed in 

 the fore-arm, where it supplies the extensor muscles and the flexor 

 metaoarpi externus. 



The Ulnar Nerve (Plates 5 and 6) derives its fibres from the dorsal 

 roots of the brachial plexus. At first it lies close behind the main 



