THE CERVICAL NERVES 



runs out alone. Three trunks upper, middle, and lower are thus formed, and, 

 as they pass beneath the clavicle, each splits into an anterior and a posterior divi- 

 sion. 1 The anterior divisions of the upper and middle trunks unite to form a cord, 

 which is situated on the lateral side of the second part of the axillary artery, and 

 is called the lateral cord or fasciculus of the plexus. The anterior division of the 

 lower trunk passes down on the medial side of the axillary artery, and forms the 

 medial cord or fasciculus of the brachiai plexus. The posterior divisions of all three 

 trunks unite to form the posterior cord or fasciculus of the plexus, which is situated 

 behind the second portion of the axillary artery. 



Relations. In the neck, the brachiai plexus lies in the posterior triangle, being covered by the 

 skin, Platysma, and deep fascia; it is crossed by the supraclavicular nerves, the inferior belly 

 of the Omohyoideus, the external jugular vein, and the transverse cervical artery. It emerges 

 between the Scaleni anterior and medius; its upper part lies above the third part of the sub- 

 clavian artery, while the trunk formed by the union of the eighth cervical and first thoracic is 

 placed behind the artery; the plexus next passes behind the clavicle, the Subclavius, and the trans- 

 verse scapular vessels, and lies upon the first digitation of the Serratus anterior, and the Sub- 

 scapularis. In the axilla it is placed lateral to the first portion of the axillary artery; it surrounds 

 the second part of the artery, one cord lying medial to it, one lateral to it, and one behind it; 

 at the lower part of the axilla it gives off its terminal branches to the upper limb. 



DESCENDING 

 BRANCH OF 



HYPOGLOSSA'. 



ANSA 

 HYPOGLOSSI 



THYROID 



AXIS 



INTERNAL 



MAMMARY 



ARTERY 



SUBCLAVIAN 



BRANCH TO 

 PHRENIC 



ANTERIOR 

 THORACIC 



FIG. 808. The right brachiai plexus with its short branches, viewed from in front. The Sternomastoid and Trapezius 

 muscles have been completely, the Omohyoid and Subclavius have been partially, removed; a piece has been sawed out 

 of the clavicle; the Pectoralis muscles have been incised and reflected. (Spalteholz.) 



Branches of Communication.- Close to their exit from the intervertebral foramina 

 the iifth and sixth cervical nerves each receive a gray ramus communicans from 

 the middle cervical ganglion of the sympathetic trunk, and the seventh and eighth 

 cervical similar twigs from the inferior ganglion. The first thoracic nerve receives 

 a gray ramus from, and contributes a white ramus to, the first thoracic ganglion. 



1 The posterior division of the lower trunk is very much smaller than the others, and is frequently derived entirely 

 from the eighth cervical nerve. 





