BRACHIAL PLEXUS 185 



of the neck, and, passing between scalenus medius and aiiticus 

 with the subclavian artery, they accompany the axillary artery 

 to the shoulder and upper limb. 



As the nerves enter the posterior triangle they form the three 

 primary cords 



First primary cord : Fifth and sixth nerves joined together. 



Second primary cord : Seventh nerve alone. 



Third primary cord : Eighth cervical and first thoracic joined 

 together. 



As soon as the three cords are formed they each divide into 

 anterior and posterior divisions to form the secondary cords, 

 which are named according to their relation to the axillary 

 artery. 



Outer cord : Anterior divisions of first and second primary 

 cords. 



Inner cord : Anterior division of third primary cord. 



Posterior cord : Posterior divisions of all three primary cords. 



The nerves supplying the shoulder and arm are derived from 

 these three cords viz. : 



Outer cord : Musculo-cutaneous, outer head of median, external 

 anterior thoracic nerves. 



Inner cord : Ulnar, inner head of median, internal anterior 

 thoracic, internal cutaneous, and lesser internal cutaneous nerves. 



Posterior cord : Circumflex, three subscapular and musculo- 

 spiral nerves. 



Before the nerves join up to form the cords, a few branches 

 are given off which are called Supraclavicular nerves to dis- 

 tinguish them from the branches derived from -the secondary 

 cords which are called the Infraclavicular nerves. 



Supraelavieular Nerves. Muscular branches to scaleni, sub- 

 clavius, and longus colli. 



Posterior scapular supplies the rhomboids and levator anguli 

 scapulas. 



Long thoracic supplies serratus magnus. It pierces scalenus 

 medius and enters the axilla between the artery and serratus 

 magnus. This nerve is also called the respiratory nerve of Bell. 



Suprascapular supplies supra- and infraspinatus and articular 

 branches to the shoulder-joint. It passes down to the superior 



