THE ANTERIOR PART OF THE NECK 241 



unite the second and third and the third and fourth nerves 

 are directed posteriorly ; and they lie on the superficial surface 

 of the upper part of the scalenus medius muscle. The first 

 loop is connected with the upper ganglion of the sympathetic 

 trunk and with the hypoglossal nerve ; and the roots of the 

 second, third and fourth nerves also are connected, by grey 

 rami, with the upper cervical sympathetic ganglion. 



The branches of the plexus are divisible into two main 

 groups, the superficial and the deep. The deep branches are 

 separable into two groups : the anterior, which run forwards 

 and the posterior, which run backwards ; and the superficial 

 branches are classified as ascending, transverse and descending. 

 The anterior group of deep branches includes : (i) the ramus 

 communicans cervicalis, and (2) the phrenic nerve. 



The posterior group of deep branches is formed by : (i) The 

 communicating branches to the accessory nerve. (2) Branches 

 of supply to (a) the sterno-mastoid from the second nerve ; 

 (b) the levator scapulae from the third and fourth ; (c) 

 the trapezius from the third and fourth ; (d) the scalenus 

 medius from the second, third, and fourth. (3) Less im- 

 portant muscular branches from the first loop to (#) 

 the rectus capitis lateralis ; (^) the rectus capitis anterior 

 (O.T. rectus capitis anticus minor); (c) the longus capitis 

 (O.T. rectus capitis anticus major). (4) Muscular branches 

 from the third and fourth nerves to the longus colli. 



The ascending group of superficial branches is formed by the 

 small occipital and great auricular nerves. The transverse 

 branch is the nervus cutaneus colli, and the descending 

 branches are the supraclavicular nerves. All the superficial 

 nerves have already been traced in the earlier stages of the 

 dissection (pp. 145, 146), but the phrenic nerve requires 

 careful consideration. 



Nervus Phrenicus. The importance of the phrenic nerve 

 depends upon the fact that it is the nerve of supply to the 

 chief muscle of respiration, the diaphragm. The majority of 

 its fibres spring from the fourth cervical nerve, but it receives 

 twigs from the third and, not uncommonly, from the fifth 

 nerve also. It descends from the neck through the superior 

 and posterior mediastinal regions of the thorax, and, after 

 piercing the diaphragm, it is distributed on its lower surface. 

 Only the cervical portion of the nerve belongs to the dis- 

 sector of the neck the remainder is displayed by the dissector 



VOL. II 16 



