i 4 2 HEAD AND NECK 



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 

 unite the second and third and the third and fourth nerves, 

 are directed backwards ; 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 ram us 

 communicans cervicalis (p. 131), and (2) the phrenic nerve. 

 (3) Less important muscular branches, from the first loop to 



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

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

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

 from the third and fourth nerves, to the longus colli. 



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. 



The ascending group of superficial branches is formed by the 

 lesser 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. 34, 35). The small muscular branches 

 require no special notice, 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 



