148 



Spinal Nerves. 



To the MM. scaleni 

 a. M. Long: colli 



' To ikett. PHRENIC. 



'POSTER. THORACIC 



SUPRA- SCAPULAR to the 

 MM. supra-, infraspinat., 

 teres minor. 



SUBSCAPULAR 



To the 



MM. subcLa>v.,pector. 

 maj., min., deltoid. 



LONG THORACIC 



To the M. serrat 



magnus 



492. Diagram of the Supra- and Infraclavicular 



Portions of the Bracliial Plexus. 



The brachial plexus is formed by the anterior branches of the 

 four lower cervical nerves and the greater part of the first dorsal. The manner in 

 which the nerves are disposed in the plexus, is liable to a great deal of variation, 

 the more frequent arrangement, however, is the following: the fifth and sixth 

 cervical nerves join together to form an upper trunk, the eighth cervical and 

 first dorsal unite to form a lower trunk, while the seventh cervical forms by 

 itself a middle trunk. Soon after passing the outer border of the scaleni muscles, 

 each trunk divides into an anterior and a posterior branch. The anterior 

 branches of the upper and middle trunks unite together to form the Tipper 

 or outer cord of the plexus ; the anterior branch of the lower trunk forms 

 by itself the 1 o w e r or inner cor d, and the posterior branches of all three 

 trunks unite to form the middle or posterior cord. Sometimes the nerves blend 

 so as to form only two principal trunks, from which the three cords are given off. 



The brachial plexus is divided into a supraclavicular and an infra- 

 clavicular portion, Pars supra- et Pars infraclavicularis. The former lies 

 in the Fossa supraclavicular Is, and its branches, besides those for the MM. scaleni 

 and M. longus colli, are the following: 



