508 NEUROLOGY. 



the thoracic cavity, and passing to the iDucr side of the brachial 

 artery, receives a filament from the sympathetic; thence it travels 

 between the two layers of the mediastinum, and reaching the 

 aponeurotic centre of the diaphragm, divides into numerous 

 branches, which are carried towards the periphery of the muscle. 



BRACHIAL PLEXUS. 



(Fig. 190.) 



The brachial plexus comprehends that large bundle of nerves 

 formed of the inferior branches of the seventh and eighth cervical, 

 the first and part of the second dorsal nerves, all of which 

 converge to the interstice between the two divisions of the 

 scalenus muscle, where they unite, and pass outwards round the 

 first rib. At and below the arm, the plexus divides into numer- 

 ous l)ranches, distributed to the muscles and teguments of the 

 anterior extremity ; the chief branches we describe as follows : — 



The Anterior scapular nerve is a large branch which 

 supplies the muscles on the dorsum of the scapula ; it turns 

 round the anterior border of the bone, a little above its neck, 

 passing under the antea-spinatus, to which and to the postea- 

 spinatus it gives twigs, terminating in the latter. 



The Thoracic nerve consists of six or seven branches of 

 unequal size and length, usually distributed to the muscles 

 between the shoulder and the trunk ; three anterior ones are 

 directed obliquely downwards, losing themselves in the muscles 

 attached to the sternum ; while of the three posterior branches, 

 one, winding I'ound the posterior border of the caput muscles, 

 becomes superficial, and is distributed to the panniculus and 

 skin ; while the remainder are distributed to the latissimus dorsi 

 and serratus magnus. 



The Subscapular nerve includes two principal cords, the 

 smaller of which goes to the subscapularis, and the larger, the 

 axillary or circumflex nerve, turning round the scapulo-humeral 

 articulation, terminates in a subcutaneous branch which descends 

 the arm. It supplies the subscapularis, teres externus, and 

 levator humeri, and furnishes articular and cutaneous filaments. 



The Radial nerve, a large branch of the brachial plexus, is 

 principally furnished by the first dorsal. It arises behind the 

 humeral artery, and is directed backwards and downwards under 

 the subscapularis and teres major muscles, being accompanied for 



