80 DISSECTION OF THE NECK. 



the clavicle, and those below that bone. The highest set end mostly in 

 muscles of the lower part of the neck and of the scapula ; whilst the other 

 set consist of the terminal branches, and are furnished to the upper limb, 

 with which they will be referred to. 



BRANCHES ABOVE THE CLAVICE. The branch of the subclavius mus- 

 cle is a slender twig, which arises from the trunk formed by the fifth and 

 sixth nerves, and is directed downwards over the subclavian artery to the 

 under surface of the muscle ; it is often united with the phrenic nerve at 

 the lower part of the neck. 



The branch of the rhomboid muscles springs from the fifth nerve in the 

 substance of the middle scalenus, and perforates the fibres of that muscle ; 

 it is directed backwards beneath the levator anguli scapulae to its destina- 

 tion. Branches are given usually from this nerve to the levator anguli 

 scapulae. 



The nerve of the serratus (posterior thoracic nerve) is contained in the 

 scalenus, like the preceding, and arises from the fifth and sixth nerves 

 near the intervertrebral foramina. Piercing the fibres of the scalenus 

 lower than the preceding branch, the nerve is continued behind the brachial 

 plexus, and enters the serratus magnus muscle on the axillary surface. 



Branches of the scaleni and longus colii muscles. These small twigs 

 are seen when the anterior scalenus is divided; they arise from the begin- 

 ning of the trunks of the nerves. 



The suprascapular nerve is larger than either of the others. It arises 

 near the subclavian branch from the cord of the plexus formed by the fifth 

 and sixth nerves. Its destination is to the muscles on the dorsum of the 

 scapula, and it will be dissected with the arm. 



Occasionally an offset from the fifth cervical trunk joins the phrenic 

 nerve on the anterior scalenus muscle. 



The CERVICAL PLEXUS is formed by the first four cervical nerves. 

 Situate at the upper part of the neck, it lies beneath the sterno-mastoid 

 muscle, and on the middle scalenus and the levator anguli scapulae. It 

 differs much from the brachial plexus, for it resembles a network more 

 than a bundle of large cords. The following is the general arrangement of 

 the nerves in the plexus : Each nerve, except the first, divides into an 

 ascending and a descending branch, and these unite with similar parts of 

 the contiguous nerves, so as to give rise to a series of arches. From these 

 loops or arches the different branches arise : 



The branches are superficial and deep. The superficial set has been 

 described with the triangular space of the neck, as consisting of ascending 

 and descending (p. 66). The ascending branches may be now seen to 

 spring from the union of the second and third nerves ; and the descending, 

 to take origin from the loop between the third and fourth nerves. The 

 deep set of branches remains to be examined : they are muscular and com- 

 municating, and may be arranged into an internal and an external series. 



INTERNAL SERIES The phrenic or muscular nerve of the diaphragm 

 (fig. 16) is derived from the fourth, or third and fourth nerves of the 

 plexus ; and it may be joined by a fasciculus from the fifth cervical nerve. 

 Descending obliquely on the surface of the anterior scalenus from the outer 

 to the inner edge, it enters the chest in front of the internal mammary 

 artery, but behind the subclavian vein, and traverses that cavity to reach 

 the diaphragm. At the lower part of the neck the phrenic nerve is joined 

 by a filament of the sympathetic, and sometimes by an offset of the nerve 

 of the subclavius muscle. 



