320 HUMAN ANATOMY. 



scalenus medius and levator anguli scapulae muscle. It gives 

 oil' : 



Superficial. 



Superficialis colli, Occipitalis minor, 



Auricularis magnus, Supraclavicular. 



Dec i). 



Communicating, Communicantes hypoglossi, 



Mu4uJar, Communicating, 



Phrenic, Muscular. 



The phrenic nerve, or internal respiratory of Bell, is derived 

 from the third and fourth cervical nerves, with a branch from 

 the fifth. It descends into the chest between the subclavian 

 artery and vein, between the pericardium and the pleura, to the 

 diaphragm, to which it is distributed. The course of the two 

 nerves differs in the thorax (vide Mediastinum). 



THE BRACHIAL PLEXUS is formed by the anterior branches 

 of the four lower cervical and the first upper dorsal nerves the 

 fifth, sixth, and seventh forming one cord, and the eighth cervical 

 and first dorsal another cord. Below the line of the clavicle, 

 both these trunks divide, the adjacent cords of the two upper 

 uniting to form the posterior, and the remaining cords forming 

 the outer and inner cords respectively, receiving their names 

 from their relative position to the subclavian artery. Each of 

 these cords again bifurcates, the adjacent divisions at the outer 

 ending of the cords uniting over the artery to form the median 

 nerve, the other divisions forming the musculo-cutaneous, ulnar, 

 circumflex, and musculo-spiral, the two latter being the divisions 

 of the posterior cord. Its branches are: 



Above the clavicle : 



Communicating, arises from the fifth cervical, and passes 

 to the phrenic ; 



Muscular, supply the scaleni, rhomboidii, longus colli, and 

 subclavius ; 



Posterior thoracic, long thoracic, or external respiratory of 

 Bell, arises by five roots from the fifth to seventh cervical nerves, 

 which unite within the scalenus medius muscle and descend to 

 supply the serratus magnus ; 



Suprascapular, passes beneath the trapezius, through the 

 suprascapular notch, to supply the shoulder-joint and supra- 

 spinatus muscle. 



Below the clavicle : 



The anterior thoracic nerves are two in number : an external 

 branch from the outer cord and an internal from the inner cord. 



