THE HEAD AND NECK 1093 



The superficial or transverse cervical nerve arises by two roots 

 from the anterior primary divisions of the second and third cervical 

 nerves, and, turning round the posterior border of the sterno- 

 cleido-mastoid muscle, it passes forwards over the muscle, lying 

 beneath the platysma myoides and the external jugular vein. 

 Having reached the anterior triangle of the neck, it divides into 

 two branches, upper and lower, which are distributed to the integu- 

 ment over the anterior triangle. The offsets of the upper branch 

 communicate freely with the inframandibular branch of the facial 

 nerv^e beneath the platysma myoides. 



The descending nerves are the suprasternal, supraclavicular, and 

 supra-acromial, and they arise in common from the third and 

 fourth cervical nerves. As they descend they form distinct nerves, 

 which lie in the roof of the subclavian triangle under cover of the 

 platysma myoides. For their distribution, see p. 298. 



Deep Group. — ^The nerves of this group are arranged in two sets — 

 external and internal. 



External Set. — ^The nerves of this set are muscular, (i) The 

 second nerve furnishes a branch to the stemo-cleido-mastoid, which 

 communicates in that muscle with the branch of the spinal portion 

 of the spinal accessory nerve. (2) The third and fourth nerves 

 furnish {a) two branches to the trapezius, which communicate in a 

 plexiform manner with the spinal portion of the spinal accessory 

 nerve beneath the upper part of the muscle ; (b) two branches to 

 the levator anguli scapulae ; and (c) branches to the scalenus medius. 



Internal Set. — ^The nerves of this set are communicating and 

 muscular. 



The communicating branches are as follows : (i) connecting 

 branches (grey rami communicantes) pass from the upper cervical 

 ganglion of the sympathetic ; (2) communicating branches pass to 

 the pneumogastric and hypoglossal nerves from the highest loop of 

 the plexus ; and (3) two rami communicantes cervicis pass from 

 the second and third nerves forwards and downwards, usually over, 

 but sometimes underneath, the internal jugular vein, and ter- 

 minate by joining the descendens cerv'icis, conjointly or separately, 

 thus forming the ansa cervicis (ansa hypoglossi). 



The muscular branches are distributed to the rectus capitis 

 lateralis, recti antici, major and minor, upper part of the scalenus 

 anticus, longus colli, and the diaphragm. The ner\'e to the dia- 

 phragm is the phrenic nerve (internal respiratory ner^'e), and, from 

 its importance, it requires a special description. 



The phrenic nerve arises, as a rule, by two roots, the larger .of 

 which is derived from the anterior primary division of the 

 fourth cervical nerve, and the other from that of the third. 

 In some cases the fifth cervical nerv^e, which enters into the 

 brachial plexus, furnishes an additional small root. In the neck 

 the nerve descends upon the scalenus anticus muscle, which it 

 crosses obliquely downwards and inwards, passing beneath the 

 tendon of the omo-hyoid muscle, the transverse cerv^ical and supra- 



