786 



THE NERVOUS SYSTEM 



the pleura. In its course between tlie pericardium and pleura it crosses in front 

 of the root of the lung. It tlien pierces the diaphragm immediately on the 

 left side of the opening for the vena cava inferior, and is distril>uted to the 

 diaphragm, the branches entering the muscle on its lower surface. On the left 

 side the ])hrenic nerve passes on to tlie left side of the aortic arch, Ijetween the latter 

 and the pleura, and in front of the inferior cervical cardiac branch of the vagus. It 

 then runs downwards between the pericardium and the })leura in front of the root 

 of the lung, taking a longer course tlian on the right side in consequence of the incli- 

 nation of the heart to the left side, and also on account of the lower level of the left 

 cupola oi the diaphragm. It pierces the diaphragm immediately to the left of the 

 attachment of the pericardium to that muscle, and is distributed to its abdominal 

 surface in a similar manner to the nerve on the right side. 



Branches. — Minute twigs are supplied (a) to the pleura; and (6) to the 

 pericardium. On the right side the nerve communicates with the diaphragmatic 

 plexus of the sympathetic, forming a small ganglion (ganglion diaphragmat- 

 icum I. 



BRACHIAL PLEXUS 



The BRACHIAL PLEXUS is formed by the anterior primary divisions of the 

 four lower cervical nerves and the greater i)art of the first thoracic nerve ; it 

 is usually joined l)y small communicating twigs from the fourth cervical and 

 second thoracic nerves. The four lower cervical nerves emerge in the interval 



Fig. 455. — Diagram of the Brachial Tlexis. 

 The posterior cord of the plexus is darkly shaded. 



FROM FOURTH CERVICAL 



FIFTH 

 CERVICAL 



SIXTH 

 CERVICAL 



HEVEXTH 

 CERVICAL x^ 

 TO SCALENI & ' \S\ 



Loyors COLLI 



EKiHTH 

 CERVICAL 

 POSTERIOR 

 THORA CIC 



FIRST 

 THORACIC 



FIRST 

 INTERCOSTAL 



sEcoyn 



THORA CIC 

 SECOND 

 INTERCOSTAL 

 THIRD 

 THORACIC 

 THIRD 

 INTERCOSTAL 



RHOMBOID NERVE 

 TO PHRENIC 



■NERVE TO SUBCLAVIUS 



SUPRASCAPULAR 



EXTERNAL ANTERIOR THORACIC 



— OUTER CORD OF PLEXUS 

 CIRCUMFLEX 

 MUSCUL O- CUT A NEO I 'S 

 MUSCULO-SPIRA L 

 INNER CORD OF PLEXUS 

 LONG 

 SUBSCAPULAR 



MEDIAN 



ULNAR 

 INTERNA L 

 CUTANEOUS 



NERVE OF 

 WRISBhRCr 



INTER COS TO- HUMERAL LATERAL CUTANEOUS 



between the anterior and nuddle scaleni muscles. The first thoracic nerve, after 

 traversing the intervertebral foramen between the first and second tlioracic vertebra', 

 appears in the first intercostal space and, after giving off the small first intercostal 

 nerve, crosses the inner margin and upper surface of the first rib ol)li(iuely, and 

 joins the eighth cervical nerve. 



The brachial plexus is divisible into four distinct stages, in the first stage all 



