Phrenic Nerve 147 



the most important of which are from the second and third for the 

 sterno-mastoid ; the influence of these nerves may render futile section 

 of the spinal accessory (p. 71) nerve in the case of spasmodic con- 

 traction of that muscle. The trapezius also receives branches from the 

 third and fourth, which, like the sterno-mastoid branch, communicate 

 with the spinal accessory. 



The phrenic comes from the third and fourth, and receives a twig 

 also from the fifth nerve, that is, from the upper part of the brachial 

 plexus. It descends into the chest over the scalenus anticus and 

 the subclavian artery, and behind the vein. It then runs in front of 

 the root of the lung, between the pleura and pericardium, and supplies 

 the diaphragm on its under-surface, giving off pleural and pericardial 

 twigs in its course. 



The left nerve is the longer, because it is pushed out of its course 

 by the pericardium ; it bears an important relation to the front of the 

 transverse aortic arch, whilst the right nerve descends on the outer 

 side of the innominate artery and the superior cava. 



Filaments of the right phrenic pass under the coronary and falciform 

 ligament , into the substance of the liver; and it is probably through 

 their influence that, in disease of the liver, pain is referred to the point 

 of the right shoulder (p. 339). The phrenic chiefly comes from the 

 fourth cervical nerve, which also gives off acromial filaments in the 

 supra-clavicular nerves, as already noted. 



In paralysis of the diaphragm, as after diphtheria, the phrenic nerve 

 may be galvanised on dragging the lower end of the sterno-mastoid 

 slightly inwards (so that the rheophore may be placed over the scale- 

 nus anticus, the outer border of which muscle corresponds to the 

 outer border of the sterno-mastoid), the other rheophore being placed 

 over the costal attachment of the diaphragm. 



L2 



