694 



THE NEKYOUS SYSTEM. 



through the brachial plexus, supply the upper limb. The second thoracic nerve 

 may contribute a trunk to this plexus, and always assists in the innervation of 

 the arm. 



PLEXUS CERYICALTS. 



The anterior rami of the first four cervical nerves are concerned in forming the 

 cervical plexus. Each nerve emerges from the vertebral canal posterior to the 



STERNO-TMVKEOID 



SUPRA-CUAV1CUUAR NERVES 



FIG. 610. THE LEFT CERVICAL PLEXUS. 



vertebral artery. Each is joined on its emergence from the intervertebral foramen, 

 at the side of the vertebral column, by a gray ramus communicans from the superior 

 cervical ganglion of the sympathetic. In the neck the cervical nerves are 

 concealed by the sterno-mastoid muscle ; in front lies the longus capitis muscle, 

 and behind are the scalenus medius, and (behind the first or sub-occipital nerve) 

 the rectus capitis lateralis. The cervical plexus is constituted by the combination 

 of the four nerves in an irregular series of loops under cover of the sterno-mastoid 

 muscle, and overlapped, in part, by the internal jugular vein. 



From the loops of the plexus the branches of distribution arise, as (a) cutaneous 

 branches to the head, neck, and shoulder ; (&) muscular branches to muscles of the 



