THE BRACHIAL PLEXUS 



1029 



communicate with the spinal accessory nerve, in the substance of the Sterno- 

 niastoid muscle, in the posterior triangle, and beneath the Trapezius. 



Muscular branches are distributed to the Sternomastoid. Trapezius, Levatof 

 anguli scapulae, and Scalenus medius. 



The branch for the Sternomastoid is derived from the second cervical; the 

 Trapezius and Levator anguli scapulae receive branches from the third and 

 fourth. The Scalenus medius is derived sometimes from the third, sometimes 

 from the fourth, and occasionally from both nerves. 



FIFTH 

 CERVlCALl 



SIXTH 



SEVENTH 



TO SCALENI i 

 LONGUS COLLI 



SECOND;J- 



THIRD' 



POSTERIOR 

 THORACIC 



FROM FOURTH CERVICAL 

 _-0 



3 *3 r 



SUPRASCAPULAR 



EXTERNAL ANTERIOR THORACIC 



INTERNAL ANTERIOR THORACIC 



CIRCUMFLEX 



MUSCULO SPIRAL 



*%:> 



^jfef-V-- 



*<?-- 



^!r as ^ 



FIG. 759. Plan of the brachi:il plexus. (Gerrish.) 



Applied Anatomy. The cervical plexus may be damaged by wounds or contusions, which 

 may or may not be associated with fracture of the clavicle. Paralysis ensues, the extent depend- 

 ing on the degree of damage. After a contusion the paralysis is apt to be temporary and to 

 b<- followed by pain and muscular spasm in the arm. Paralysis of the arm due to plexus injury 

 may be partial or complete. In some cases there is complete motor palsy and partial sensor 

 palsy, the sensor impulses passing along undamaged collaterals. In certain spasmodic diffi- 

 culties the surgeon occasionally stretches the cervical plexus. It is reached by an incision at the 

 posterior margin of the Sternomastoid muscle. This incision begins two inches below the level 

 of the tip of the mastoid and is carried downward for three inches. 



THE BRACHIAL PLEXUS (PLEXUS BRACHIALIS) (Figs. 757, 758). 



The brachial plexus is formed by the union of the anterior primary divisions 

 of the lower four cervical nerves and the greater part of the first thoracic nerve, 

 receiving usually a fasciculus from the fourth cervical nerve, and frequently one 

 from the second thoracic nerve. It extends from the lower part of the side of the 

 neck to the axilla. It is very broad, and presents little of a plexiform arrangement 

 at its commencement. It is narrow opposite the clavicle, becomes broad and 

 forms a more dense interlacement in the axilla, and divides opposite the coracoid 

 process into numerous branches for the supply of the upper limb. The nerves 

 which form the plexus are all similar in size, and their mode of communication is 

 subject to considerable variation, so that no one plan can be given as applying to 



