CERVICAL NERVES 783 



niedius, where tlie tliird unites with the see(jiid and fourth nerves, eoni})letin^ the 

 plexus. 



The lower four cervical nerves increase rapidly in size from the fifth to the 

 eighth, and unite with the greater part of the first thoracic nerve to fomi the 

 brachial plexus. Each of these nerves is connected by one or two twigs to the 

 cervical sympathetic. 



cp:rvical plexl^s 



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

 cervical plexus in the following manner: the second and third nerves are connected 

 hy ascending and descending branches with one another, and with the first and 

 fourth nerves. In this way a series of three loops is formed. The fourth nerve is 

 also connected with the brachial plexus by a descending twig. The plexus lies in 

 the upper part of the side of the neck, upon the scalenus medius muscle, and 

 under cover of the u})per part of the sterno-mastoid. The branches of the plexus 

 are classified into a superficial and a deep series. The superficial series is sub- 

 divided into ascending, transverse, and descending branches; the deep series into 

 external and internal Ijranches. 



Superficial Branches 



Ascending branches. — 1. The lesser occipital nerve is derived from the 

 second cervical. It i)asses backwards and slightly ui)wards under cover of the 

 sterno-mastoid muscle to reach the posterior border of that muscle. It then ascends, 

 running parallel to the posterior l)order of the muscle, being occasionally overlapped 

 liy it, and passes on to the scalp, where it divides into auricular, mastoid, and 

 occi{)ital l)ranches. (a) The auricular branch runs upwards and slightly forwards 

 to reach the integument on the jjosterior and up])er part of the pinna, and is dis- 

 tributed there. (6) The mastoid branch is distributed to the skin covering the 

 base of the mastoid process, (c) The occipital branches ramify over the occipi- 

 talis muscle, and are distributed to the skin of the scalp; they communicate with 

 one another and wath the great occipital nel've. The branches of the small occipital 

 nerve anastomose with twigs of the posterior auricular, great auricular, and great 

 occipital nerves. 



2. The great auricular nerve arises by two roots, one from the second, and 

 the other from the third cervicid nerve. It acconi])anies the lesser occipital nerve 

 as far as the posterior border of the sterno-mastoid. and then Avinds round that 

 muscle, and crosses it obliquely. In this course it runs upwards and forwards 

 towards the tip of the mastoid process, and is covered by the skin, sujierficial fascia, 

 and platysma. At a point about the centre of its course across the sterno-mastoid 

 muscle, it begins to divide into branches, which diverge from one another as the}' 

 approach the level of the mastoid ])rocess, forming mastoid, auricular, and facial 

 branches, (a) The mastoid branch is small, and is distributed to the integument 

 covering the mastoid process. It anastomoses with the ])osterior auricular and 

 small occipital nerves, (b) The auricular branches are three or four stcnit twigs 

 which anastomose with the l)ranches of the posterior auricular nerve; they cross 

 the superficial surface of the posterior auricular branch of the facial, and are 

 distributed to the skin on the back of the pinna with the exception of its upi)ermost 

 j>art. One or two twigs pass through fissures in the cartilage of the ear, and are 

 distributed to the integument on the outer surface of the lobule and the outer 

 surface of the loAver part of the helix and antihelix. (c) The facial branches pass 

 upwards and forwards among the su|)erticial lobules of the parotid and ^u])ply the 

 skin over that gland and immediately in frcMit of it, and they anastomose in the 

 substance of the gland with the cervico-facial division of the facial nerve. In some 

 cases fine twigs may l)e traced forwards nearly to the angle of the mouth. 



Transverse branch. — Tiie superficial cervical nerve arises from the second 

 and tliird nerves, and api)ears at the i)osterior border of the sterno-mastoid, a 

 little below^ the great auricular nerve. It jjasses transversely across the sterno- 

 mastoid under cover of the integuments, platysma, and external jugular vein. It 



