54 HEAD AND NECK 



given off from the roots, the trunks and the cords ; and the 

 roots are connected with the middle and lower ganglia of the 

 cervical part of the sympathetic trunk by grey rami communi- 

 cantes. The branches given off from the roots are twigs of 

 supply to the longus colli, the scalenus anterior, the scalenus 

 inedius, and the scalenus posterior, the roots of origin of the 

 long thoracic nerve, which supplies the serratus anterior 

 (O.T. magnus) and the dorsal scapular nerve (O.T. nerve to 

 the rhomboids). The roots of the long thoracic nerve spring 

 from the fifth, sixth, and seventh nerves ; the upper two 

 pierce the scalenus medius and the lowest passes anterior to 

 that muscle. The three unite, behind the trunks of the 

 plexus, to form the stem of the nerve, which descends behind 

 the cords of the plexus into the axilla. The dorsalis scapulae 

 nerve arises from the lateral border of the fifth nerve ; it 

 disappears under cover of the levator scapulae and supplies 

 the two rhomboid muscles, and, sometimes, the levator 

 scapulae. 



The branches from the trunks of the plexus are the supra- 

 scapular nerve and the nerve to the subclavius. They both 

 spring from the upper trunk. The collateral branches of the- 

 three cords of the plexus are (i) from the lateral cord: the 

 lateral anterior thoracic nerve; (2) from the posterior cord: 

 the upper and lower subscapular nerves and the thoraco- 

 dorsal nerve (O.T. long subscapular) ; and (3) from the 

 medial cord : the medial anterior thoracic, the medial 

 cutaneous nerve of the arm (O.T. lesser internal cutaneous) 

 and the medial cutaneous nerve of the forearm (O.T. internal 

 cutaneous). 



The Position of the Brachial Plexus. The plexus lies (i) in 

 the lower and anterior part of the posterior triangle of the 

 neck, partly above and partly below the posterior belly of the 

 omo-hyoid ; (2) posterior to the clavicle ; and (3) in the axilla. 

 Above the clavicle it is covered by the skin, the superficial 

 fascia and the platysma, branches of the supraclavicular 

 nerves, the first layer of deep fascia, the external jugular vein, 

 and the terminal parts of the transverse cervical and trans- 

 verse (supra) scapular veins; the second layer of deep 

 cervical fascia, the transverse cervical artery, the posterior 

 belly of the omo-hyoid, the nerve to the subclavius, and the 

 third part of the subclavian artery. Behind the clavicle it is 

 crossed superficially by the transverse scapular artery (O.T. 



