103 2 THE NER VE SYSTEM 



arise from the four lower cervical nerves at their exit from the interverrebr:i1 

 foramina. 



The nerve to the Subclavius (n. subdavius) is a small filament which arixc* 

 from the fifth cervical at its point of junction with the sixth nerve; it descends 

 in front of the third part of the subclavian artery to the Subclavius muscle, and is 

 usually connected by a filament with the phrenic nerve. 



The posterior scapular nerve (n. dorsal is scapulae) (Figs. 757 and 759) arises 

 from the fifth cervical, pierces the Scalenus medius, and passes beneath the Leva tor 

 anguli scapulae, which it occasionally supplies to the Rhomboid muscles. 



The Long Thoracic or the External Respiratory Nerve of Bell or Posterior Thoracic 

 Nerve (/?. thoracalis longus) (Figs. 757 and 764) supplies the Serratus map;nus 

 muscle, and is remarkable for the length of its course. It usually arises by three 

 roots from the fifth, sixth, and seventh nerves, but the root from the seventh 

 may be absent. The roots from the fifth and sixth nerves pierce the Scalenus 

 medius, while that from the seventh emerges in front of that muscle. The nerve 

 passes down behind the brachial plexus and the axillary vessels, resting on the 

 outer surface of the Serratus magnus. It extends along the side of the thorax 

 to the lower border of that muscle, supplying filaments to each of the muscular 

 dictations. 



The Suprascapular Nerve (n. suprascapular is) (Figs. 759 and 764) arises from the 

 trunk formed by the fifth and sixth cervical nerves; passing obliquely outward 

 beneath the Trapezius and the Omohyoid, it enters the supraspinous fossa below 

 the transverse or suprascapular ligament, passes beneath the supraspinatus 

 muscle, and curves around the external border of the spine of the scapula to the 

 infraspinous fossa. In the supraspinous fossa it gives off two branches to the 

 Supraspinatus muscle, and an articular filament to the shoulder-joint; and in 

 the infraspinous fossa it gives off two branches to the Infraspinatus muscle, 

 besides some filaments to the shoulder-joint and scapula. 



The Infraclavicular Branches (Figs. 758 and 759) are derived from the three 

 cords of the brachial plexus. The fasciculi of which they are composed may be 

 traced through the plexuses to the spinal nerves from which they originate. They 

 are as follows: 



[ Musculocutaneous 5, (),('. 



External anterior thoraci 5,6,7,C. 



i Outer head of median 6, 7, ( . 



( Internal anterior thoracic 8, C. 1,T. 



I Internal cutaneous 8, C. 1,T. 



Inner cord . -! Lesser internal cutaneous (8, C.)1,T. 



I Ulnar 8,C.1,T. 



I Inner head of median 8, C. 1 , T. 



f Upper subscapular 5, 6, C. 



I Middle " 5, 6, 7, C. 



Posterior cord -> L ower 5, 6, C. 



I Circumflex o, (>, C. 



I Musculospiral (5), 6, 7, 8, C. (1, T). 



These branches from below the clavicle may be arranged according to the 

 parts they supply: 



To the thorax Anterior thoracic. 



To the shoulder f Subscapulars. 



\ Circumflex. 

 f Musculocutaneous. 

 , Internal cutaneous. 



To the arm, forearm, and hand . \ Lesser internal cutaneous. 



Median. 

 Ulnar. 

 Musculospiral. 



