980 



THE NERVOUS SYSTEM 



anastomoses with the phrenic of the opposite side in front of the pericardium; others descend 

 between the sternal and costal attachments of the diaphragm into the abdomen, where some of 

 them supply the diaphragm and others descend in the falciform ligament to the peritoneum on 

 the upper surface of the liver. The posterior branch passes through the vena caval opening and 

 ramifies upon the lower surface of the diaphragm, anastomosing with the diaphragmatic plexus 

 of the sympathetic, and its terminal branches supply the muscular fibres of the right half of 

 the diaphragm, the inferior vena cava, and the right suprarenal gland. 



The left phrenic nerve divides into several branches. One of the most anterior branches 

 anastomoses with the right phrenic nerve; the others pierce the diaphragm and ramify on its 

 under surface, where they anastomose with filaments of the left diaphragmatic plexus of the 

 sj-^mpathetic and supply the left half of the diaphragm and the left suprarenal gland. The left n; 

 phrenic nerve is considerably longer than the right nerve, partly on account of the lower level 

 of the diaphragm on the left side, and partly on account of the greater convexity of the left; 

 side of the pericardium. 



THE BRACHIAL PLEXUS 



The brachial plexus (figs. 751, 754, 755) is formed by the anterior primary »■ 

 divisions of the four lower cervical nerves and the greater part of that of the: 



Fig. 



Fifth cervical 



Sixth cervical 



Seventh cervical 



To scaleni and 



longus colli 



Eighth cervical 



Long thoracic 

 First thoracic 



First intercostal 

 Second thoracic 



Second intercostal 

 Third thoracic 



Third intercostal 



754. — Diagram of a Common Form of Brachial Plexus. 

 The posterior cord of the plexus is darkly shaded. 

 -From fourth cervical 



-Nerve to subclavius 



Suprascapular 



Anterior thoracic nerves 



Lateral cord of plexus 



Axillary (circumflex) 

 Musculo-cutaneous 



Radial (musculo-spiral) 



Medial cord of plexus 



Thoraco-dorsal 

 Median 



Ulnar 



Medial antibrachial 

 cutaneous 



Medial brachial cuta- 

 neous (nerve of 

 Wrisberg) 



Intercosto-brachial 



Lateral cutaneous 



first thoracic nerve. It is usually joined by small twigs from the fourth cervicall 

 and second thoracic nerves. 



The anterior ])rimary divisions of the lower four cervical nerves, after passing 

 dorsal to the vertebral artery and between the anterior and posterior parts of the 

 intertransverse muscles, pass into the posterior triangle in the interval between 

 the adjacent borders of the anterior and middle scalene muscles, where the fifth 

 and sixth nerves receive a grey ramus communicans each from the middle cervical 

 sympathetic gangUon, and the seventh and eighth nerves each receive a grey 

 ramus from th(! inferior cervical sympathetic ganghon. The first thoracic is 

 connected by two rami communicantcs with the first thoracic sympathetic gang- 

 lion, and it divides into a smaller and a larger branch. The smaller branch passes 

 along the intercostal space as the first intercostal nerve, and the larger branch, 

 after being joined l)y a twig from the second thoracic nerve, passes upward and 

 lateralward, in front of the neck of the first rib and behind the apex of the pleural 

 sac, into the; lower part of the posterior triangle of the neck, where it takes part in 

 the formation of the plexus. 



The anterior primary divisions of those cervical nerves that form the brachial 

 plexus may be considered as tyi)ically giving off anterior and posterior branches, 



