BRACHIAL PLEXUS. 



567 



Commanicitti-ny m"0k Phrenic 



Supra -Scapular 

 -Line of Clavicle 



form arrangement at its commencement, narrow opposite the clavicle, broad and 

 presenting a more dense interlacement in the axilla, and dividing opposite the 

 coracoid process into numerous branches for the supply of the upper limb. These 

 nerves are all similar in size, and their mode of union in the formation of the 

 plexus is the following. The fifth and sixth nerves unite near their exit from 

 the spine into a common trunk ; the seventh nerve joins this trunk near the outer 

 border of the Middle scalenus ; and the three nerves thus form one large single 

 cord. The eighth cervical and first dorsal nerves unite beneath the Anterior 

 scalenus into a common trunk. Thus two large trunks are formed, the upper one 

 by the union of the fifth, sixth, and seventh cervical ; and the lower one by the 

 eighth cervical and first dorsal. These two trunks accompany the subclavian 

 artery to the axilla, lying upon its outer side, the trunk formed by the union of the 

 last cervical and first dorsal 



being nearest to the vessel. F[ S- 285. Plan of the Brachial Plexus. 



Opposite the clavicle, and 

 sometimes in the axilla, 

 each of these cords gives 

 off a fasciculus, which 

 uniting, a third trunk is 

 formed, so that in the 

 centre of the axilla three 

 cords are found, one lying 

 on the outer side of the 

 axillary artery, one on its 

 inner side, and one behind. 

 The brachial plexus com- 

 municates with the cer- 

 vical plexus by a branch 

 from the fourth to the 

 fifth nerve, and with the 

 phrenic by a branch from 

 the fifth cervical, which 

 joins that nerve on the 

 Anterior scalenus muscle: 

 the cervical and first dor- 

 sal nerves are also joined 

 by filaments from the mid- 

 dle and inferior cervical 

 ganglia of the sympathetic, 

 close to their exit from the 

 intervertebral foramina. 



Relations. In the neck, the brachial plexus lies at first between the Anterior 

 and Middle scaleni muscles, and then above and to the outer side of the subclavian 

 artery ; it then passes beneath the clavicle and Subclavius muscle, lying upon the 

 first serration of the Serratus magnus and Subscapularis muscles. In the axilla, 

 it is placed on the outer side of the first portion of the axillary artery ; it surrounds 

 the artery in the second part of its course, one cord lying upon the outer side of 

 that vessel, one on the inner side, and one behind it ; and at the lower part of the 

 axillary space gives off its terminal branches to the upper extremity. 



The Branches of the Brachial Plexus may be arranged into two groups, viz., 

 those given off above the clavicle, and those below that bone. 



(1.) BRANCHES ABOVE THE CLAVICLE. 



Communicating. 

 Muscular. 



Posterior thoracic. 

 Suprascapular. 



