638 



SPINAL NERVES. 



tfrtm 



mmitnientcTitf with Phrenic 



Sl *P rtt -Scapular 



tf Ciaviclt 



upper limb. The nerves which form the plexus are all smaller in size, and 

 their mode of communication 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 



Fig. 349. Plan of the Brachial Plexus. border of the Middle Scalenus; 



and the three nerves thus form 

 one large single cord. The 

 eighth cervical and first dorsal 

 nerves unite behind the Ante- 

 rior 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 ar- 

 tery 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. Opposite the 

 clavicle, and sometimes in the 

 axilla, each of these cords gives 

 off a fasciculus, by the union 

 of which a third trunk is formed, 

 so that in the middle 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. 1 

 The brachial plexus communi- 

 cates with the cervical plexus by a branch from the fourth to the fifth nerve, 

 and with the phrenic nerve by a branch from the fifth cervical, which joins 

 that nerve on the Anterior Scalenus muscle. The cervical and first dorsal 

 nerves are also joined by filaments from the middle 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 sub- 

 clavian artery; it then passes behind the clavicle and Subclavius muscle, lying 

 upon the first serration of the Serratus Magnus and the 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. 



Branches. The branches of the brachial plexus are arranged into two groups, 

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



BRANCHES ABOVE THE CLAVICLE. 



Communicating. Posterior thoracic. 



Muscular. Suprascapular. 



The communicating branch with the phrenic is derived from the fifth cervical 

 nerve ; it joins the phrenic on the Anterior Scalenus muscle. 



1 This is the most common mode of formation of the plexus ; hut it is also very common for 

 the third, or posterior, cord to be formed by the seventh cervical nerve, running undivided, and 

 receiving a branch from each of the other cords. 



