THE HEAD AND NECK 



1097 



simple by arranging it into four stages, namely (i) nerve-roots, 

 (2) nerve-trunks, (3) divisions of nerve-trunks, and (4) nerve- 

 cords. 



First Stage.— The nerves which form the plexus are the anterior 

 primary divisions of the fifth, sixth, seventh, and eighth cervical, 

 and the greater part of that of the first thoracic. Superiorly the 

 plexus is reinforced by a small descending branch from the fourth 

 cervical, which joins the fifth, and inferiorly it is occasionally re- 

 inforced by a branch from the second thoracic, which joins the first. 

 As regards the first thoracic nerve, the part of it which does not join 

 the plexus, and which is of small size, enters the first intercostal 

 space to become the first intercostal nerve. The nerves, as they 



To Cervical Plexus 



To Brachial Plexus^ 



Third Root of Phrenic (inconstant) 

 Nerve to the Rhomboids *" 

 Nerve to Subclavius 

 Suprascapular - 



4.C. 



5.C 



Externa] Anterior Thoracic 



Circumflex 

 Musculo-spiral 



Outer Root of Median 



Musculo-cutaneous 



Median 



2.T. 



' Posterior Thoracic (Ext. 

 , Respiratory N. of Bell) 



\ \ \ First Intercostal 



N \ ■ Upper or Short Subscapular 

 \ Internal Anterior Thoracic 

 '\ Middle or Long Subscapular 

 \ Lower Subscapular 



Nerve of Wrisberg 



' Inner Root of Median 

 ; \ Internal Cutaneous 



'Ulnar 



Fig. 446. — The Brachial Plexus. 



( Yellow = Spinal Nerves and their Branches ; Blue=Trunks ; Red =Outer Cord 

 Purple dinner Cord ; Grey = Posterior Cord.) 



emerge at the side of the neck, are placed between the scalenus 

 anticus and scalenus medius. 



Second Stage. — ^The fifth and sixth cervical nerves join at the 

 outer border of the scalenus anticus to form the upper trunk ; the 

 seventh cervical remains meanwhile single, and forms the middle 

 trunk ; and the eighth cervical and greater part of the first thoracic 

 unite between the scalene muscles to form the lower trunk. There 

 are thus three trunks — upper, middle, and lower. 



