SHOULDER AND ARM. 



tween the Scaleni, anticus and medius, and quickly unites in 

 primary cords, the first being formed by the fifth and sixth 

 cervical, the second by the seventh cervical, and the third by 

 the eighth cervical and first dorsal ; at the same time each cer- 

 vical nerve divides into two trunks, ventral and dorsal. Then 

 passing under the clavicle these trunks unite in secondary 

 cords, named from their relation to the axillary artery. The 

 outer cord, on the outer side of the artery, is formed by the 

 ventral trunks of the fifth, sixth, and seventh cervical; the 

 inner cord, on its inner side, by the ventral trunk of the eighth 

 cervical and the whole first thoracic; and the posterior cord, 

 placed behind it, by the dorsal trunks of the lower four cervical 

 nerves. [622] 



Above the clavicle (supraclavicular nerves} the branches are 

 as follows : Twigs from the lower four cervicals, near the fora- 

 mina, to the Longus colli and all the Scaleni. A branch from 

 the fifth cervical to the phrenic. A branch from the first 

 primary cord to the Subclavius, descending over the sub- 

 clavian artery and often communicating with the phrenic. 

 Posterior scapular: Arising from the fifth cervical, near the 

 foramen, this pierces the Scalenus medius, appears in the pos- 

 terior triangle and descends along the vertebral border of the 

 scapula, under and supplying the Levator anguli scapula? and 

 Rhomboids. Long thoracic : This arises from the fifth, sixth, 

 and seventh cervicals, at the foramina, by three roots; it 

 pierces the Scalenus medius in one or two trunks and descends 

 behind the plexus, then between the axillary artery and upper 

 edge of the Serratus magnus, and then over the outer surface 

 of the Serratus magnus, which it supplies. Suprascapular : 

 Arising from the back of the first primary cord, this runs 

 downward and outward above the plexus, and through the 

 suprascapular foramen, where it supplies the Supraspinatus ; 

 it then runs in the great scapular notch to supply the Infra- 

 spinatus; branches supply the shoulder joint. [624] 



Below the clavicle (infraclavicular nerves) the outer cord 

 11 [161] 



