THE BRACHIAL PLEXUS 



981 



except that the fifth and sixth nerves often unite before branching and give off 

 their posterior branches as a common trunk, and the eighth nerve often receives 

 its branch from the first thoracic nerve before giving off its posterior branch. 



It is on account of this variation in the point of union of the fifth and sixth 

 cervical nerves and of the eighth cervical and first thoracic nerves that so many- 

 different forms of the plexus have been pictured and described. But if the differ- 

 ences in primary branching be borne in mind, the formation of the plexus is always 

 uniform and simple, notwithstanding its different appearances. 



FlG. 755. — The Brachial Plexus and its Branches of the Region of the Neck and 

 Shoulder. (After Toldt, "Atlas of Human Anatomy," Rebman, London and New York.) 



Internal jugular vein 

 Phrenic / / 



Branch to levator scapulae ' / - ' \ 



Anterior branch of cervical V 



Suprascapular z' *, 



Posterior 

 thoracic 



Dorsal scapular 



Long thoracic 



Supra-clavicular 



portion of plexus 



Subscapular 



Auxiliary and radial 



Twig to coraco-brachialis 



Muscular 



branches of 



axillary 



'/^_ Descendens cer- 



" vicalis (hypoglossi) 



Sterno-nyoideus 



and sterno- 



thyreoideus 



Subclavian 

 muscle and 

 , -^' nerve 

 "W ^Anterior 

 ^^ thoracic 



Long thoracic to 

 serratus anterior 

 \^ Thoraco-dorsal to 

 latissimus dorsi 



Lateial / 

 antibrachial ' 

 cutaneous 



Brachial artery 

 \ Ulnar 



^^ Medial antibrachial 

 ^^ cutaneous 

 '* Median 



Three cords are formed from these branches in the following manner: — (1) 

 The lateral (outer) cord [fasciculus lateralis] is formed by the anterior branches of 

 the fifth, sixth, and seventh nerves; (2) the medial (inner) cord [fasciculus medi- 

 alis], by the anterior branches of the eighth cervical and first thoracic nerves; and 

 (3) the posterior cord [fasciculus posterior], by the posterior branches of all of these 

 cervical nerves. 



Relations. — The plexus extends from the lateral border of the scalenus anterior, where the 

 roots of its constituent nerves appear, to the lower border of the pectorahs minor, where each 



