ANATOMY AND PHYSIOLOGY OF THE BRAIN 381 



The anterior branches of the upper and middle 

 trunks form the outer cord of the plexus; the anterior 

 branch of the lower, the inner cord; of the posterior 

 cord it is variously stated that the posterior branches of 

 all three trunks form it, or that the posterior branches 

 of the upper and middle trunks form it, while the 



FIG. 136 



V Cervical 



Anterior division of Upper Trunk 



External Anterior Thoracic 

 Posterior division of Upper Trunk 



Middle and Lo 

 Sub-scapular 



Circumflex 



Anterior division of Lower Trunk 

 Posterior division of Lower Trunk 



Internal Anterior Thoracic 



Lesser Internal Cutai, 



Internal Cutu 



Musculu-cutaneuus 



Ulnar/ 

 Musculo-spiral' 



Plan of the brachial plexus. (Gray.) 



posterior branch of the lower trunk joins the musculo- 

 spiral nerve. It is altogether a matter of dissection. 



The plexus is at first between the anterior and middle 

 scaleni, then above and external to the subclavian 

 artery. It passes behind the clavicle and subclavius, 

 lying on the subscapularis and serratus magnus muscles. 

 The cords lie external to the first part of the axillary 



