510 CERVICAL NERVES. 



ply of the muscles and integuments on the back part of the head 

 and neck . 



The Nerves of the Diaphragm, 



Are generally denominated the Phrenic. The principal 

 root of each of them is commonly derived from the third cer- 

 vical nerve, but frequently the second and the fourth cervical 

 nerves contribute to their formation ; they are sometimes also 

 joined by a twig which is derived from the ninth pair. 



Each nerve proceeds down the neck, between the rectus 

 capitis major and the scalenus anticus, and continues across 

 the fore part of the latter muscle ; it descends into the thorax 

 within the anterior end of the first rib, between the sub- 

 clavian vein and the artery. It sometimes receives a twig 

 from the fifth cervical nerve, and a twig passes between it and 

 the great sympathetic. After entering the thorax, they de- 

 scend, attached to the mediastinum, before the root of the 

 lungs. In consequence of the projection of the point of the 

 heart to the left, the course of the left is a little different from 

 that of the right ; that of the right proceeding in a more per- 

 pendicular direction. When they arrive at the diaphragm, 

 they divide into many ramifications, which have a radiated 

 arrangement, and terminate on the fibres of that muscle, both 

 on the upper and lower surface. Some fibres from each nerve 

 are continued downward, and communicate in the abdomen with 

 the fibres of the sympathetic. 



The descending branches may readily be traced into 

 the phrenic and solar plexus. Those of the right phrenic 

 nerve may in addition be traced into the hepatic plexus. Upon 

 the branches of this nerve in the upper surface of the dia- 

 phragm, I have occasionally found distinct ganglia deve- 

 loped. 



The Fourth, Fifth, Sixth and Seventh Cervical Nerves, 



May be comprised in one description. They pass off suc- 

 cessively from the medulla spinalis between the vertebrae, 

 like the other nerves. Their Posterior Branches are generally 



