240 



HEAD AND NECK 



followed ; they may cross either superficial or deep to the internal jugular 

 vein. Then the phrenic nerve, which springs from the fourth cervical 

 nerve, and receives additional twigs from the third and fifth nerves, must 

 be followed downwards and anteriorly till it disappears under cover of the 

 lower part of the internal jugular vein. It lies upon the surface of the 

 scalenus anterior and passes deep to the omo-hyoid muscle and the trans- 

 verse cervical and transverse scapular arteries. Running parallel with, 

 and anterior to it, is the ascending cervical branch of the inferior thyreoid 

 artery. 



Small occipital i R 



n 



Great auricular 



Nervus cutaneus coll 



Branch to levator 

 scapulae 



Branch to levator 

 scapulae 



Descending trunk / Co mmuni- 



Hypoglossal 



To genio-hyoid 



c.c || Thyreo-hyoid nerve 



Descendens hypoglossi 



Ansa hypoglossi 



3 hrenic 



FIG. 98. Diagram of the Cervical Plexus and the Ansa 

 Hypoglossi. 



I, II, III, IV. Anterior branches of the upper four cervical nerves. 



R. Branches to recti and longus capitis. 

 S. M. Branches to the sterno-mastoid. 

 C.C. Rami communicantes cervicales. 



C.H. Communicating branch to hypo- 

 glossal. 



This diagram shows that the descendens hypoglossi, the branch to the 

 thyreo-hyoid, and in all probability the branches to the genio-hyoid, are 

 composed of fibres given to the hypoglossal by the communicating twigs 

 it receives from the first cervical nerve. 



Plexus Cervicalis. This is a looped plexus formed by 

 the first four cervical nerves. It lies in the upper part of 

 the side of the neck under cover of the sterno-mastoid. The 

 upper loop of the plexus, which connects the first and second 

 nerves together, is directed forwards and lies between the 

 internal jugular vein anteriorly, and the transverse process of 

 the atlas posteriorly. The second and third loops, which 



