636 THE CERVICAL NERVES AND PLEXUS. 



CERVICAL NERVES. 



The anterior divisions of the four upper cervical nerves form the cervical 

 plexus. They appear at the side of the neck between the scalenus medius 

 and rectus anticus major muscles. They are each connected by a commu- 

 nicating filament with the first cervical ganglion of the sympathetic nerve, 

 or with the cord connecting that ganglion with the second. 



The anterior divisions of the four lower cervical nerves, larger than those 

 of the upper four, appear between the scaleni muscles, and, together with 

 that of the first dorsal, go to form the brachial plexus. They are each 

 connected by a filament with one of the two lower cervical ganglia of the 

 sympathetic, or with the plexus on the vertebral artery. 



The anterior divisions of the first and second nerves require a notice 

 separately from the description of the nerves of the cervical plexus. 



SUBOCCIPITAL NERVE. 



The anterior primary division of the first nerve runs forwards in a groove 

 on the atlas, and bends downwards in front of the transverse process of that 

 vertebra to join the second nerve. In this course forwards it lies beneath 

 the vertebral artery, and at the inner side of the rectus lateralis muscle, to 

 which it gives a branch. As it crosses the foramen in the transverse process 

 of the atlas, the nerve is joined by a filament from the sympathetic ; and 

 from the arch, or loop of the atlas, which it makes in front of the transverse 

 process, branches are supplied to the two anterior recti muscles. Short 

 filaments connect this part of the nerve with the pneumo-gastric, the hypo- 

 glossal, and the sympathetic nerves. 



Valentin notices filaments distributed to the articulation of the occipital bone with 

 the atlas, and to the mastoid process of the temporal bone. , 



SECOND CERVICAL NERVE. 



The anterior division of the second cervical nerve, beginning between the 

 arches of the first two vertebrae, is directed forwards between their trans- 

 verse processes, being placed outside the vertebral artery, and beneath the 

 iutertransverse and other muscles fixed to those processes. In front of the 

 intertransverse muscles the nerve divides into an ascending part, which 

 joins the first cervical nerve, and a descending part to the third. 



V . 



CERVICAL PLEXUS. 



The cervical plexus is formed by the anterior divisions of the first four 

 cervical nerves, and distributes branches to some of the muscles of the neck, 

 and to a portion of the integument of the head and neck. It is placed 

 opposite the first four vertebras, beneath the sterno-mastoid muscle, and rests 

 against the middle scalenus muscle and the levator auguli scapuhe. The 

 disposition of the nerves in the plexus is easily recognised. Each nerve 

 except the first, branches into au ascending and a descending part : and 

 these are united in communicating loojps with the contiguous nerves. From 

 the union of the second and third nerves, superficial branches are supplied 

 to the head and neck ; and from the junction of the third with the fourth, 

 arise the cutaneous nerves of the shoulder and chest. Muscular and com- 

 municating branches spring from the same nerves. 



The branches of the plexus may be separated into two sets a superficial 



