286 THE SPINAL NERVES. 



of the nerves in the plexus is as follows : Each nerve, except the first, divides into 

 an ascending and a descending part ; and these are united in communicating loops 

 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 some of the cutaneous nerves of the shoulder and 

 chest. Muscular and communicating branches spring from the same nerves. 



The BRANCHES of the plexus may be divided into two sets a superficial and 

 deep ; the superficial consisting of those which perforate the cervical fascia and 

 supply the integument ; the deep comprising branches which are distributed for 

 the most part to the muscles. The superficial nerves may be subdivided into 

 ascending and descending ; the deep nerves into an internal and an external series. 



SUPERFICIAL ASCENDING BRANCHES. 



Small occipital nerve. The small occipital nerve varies in size, and is 

 occasionally double. It springs from the second and third (sometimes only the 

 second) cervical nerves, and is directed almost vertically to the head along the 

 posterior border of the sterno-mastoid muscle, giving off in its course twigs to the 

 skin over the upper portion of the posterior triangular space. Having perforated 

 the deep fascia near the cranium, the small occipital nerve ascends to the scalp 

 between the ear and the great occipital nerve, and ends in cutaneous filaments 

 which extend upwards to somewhat above the level of the ear. It communicates 

 with branches from the great occipital, great auricular and posterior auricular nerves, 

 and it supplies an auricular branch which is distributed to the upper part of the ear 

 on its inner aspect. 



Varieties. The small occipital nerve is sometimes directed backwards across the posterior 

 triangle of the neck, and perforates the trapezius muscle close to its upper border, before 

 ascending 1 to the head. The auricular branch is occasionally derived from the great occipital 

 nerve. The small occipital is sometimes much reduced in size and distributed solely to the 

 skin of the neck, its place on the head being- taken by branches of the great occipital nerve. 



Great auricular nerve. Arising from the second and third cervical nerves, 

 this, the largest of the ascending branches of the plexus, winds round the hinder 

 border of the sterno-mastoid, and is directed obliquely upwards between the platysma 

 myoides muscle and the deep fascia of the neck towards the lobule of the ear. A 

 little below the latter the nerve gives a few small offsets to the face, and then ends 

 in auricular and mastoid branches. 



(a) The auricular branches are directed to the back of the auricle, on which they 

 ramify, and are connected with twigs derived from the posterior auricular branch 

 of the facial nerve. One offset reaches the outer surface of the ear by a fissure 

 between the antihelix and the concha. A few filaments are supplied likewise to the 

 outer part of the lobule. 



(#) The mastoid branch ramifies in the integument over the upper end of the 

 sterno-mastoid muscle and the mastoid process, and communicates with the 

 posterior auricular and small occipital nerves. 



(c) The facial branches are distributed to the integument of the face over the 

 parotid gland. Some slender filaments penetrate into the substance of the gland, 

 and communicate with the lower division of the facial nerve. 



Varieties. The great auricular nerve may arise solely from the third, or from the third and 

 fourth cervical nerves (Henle). The mastoid branch is often a separate offset of the plexus, 

 ascending between the great auricular and small occipital nerves (fig. 191, 13). 



Superficial cervical nerve (n. subcutaneus colli). This nerve takes origin, 

 usually in common with the great auricular, from the second and third cervical 



