380 THE NERVE SYSTEM 



They are larger than the posterior. Each division is 

 connected with the sympathetic ganglia along the 

 vertebral column, by means of nerve trunks called 

 rami communicantes. (See Sympathetic System, p. 

 385.) 



THE CERVICAL PLEXUS. The cervical plexus is 

 formed by the anterior divisions of the upper four 

 cervical nerves, which emerge between the scalenus 

 medius and rectus anticus major. It lies upon the 

 scalenus medius and levator anguli scapulae, beneath 

 the sternomastoid. Each nerve except the first 

 divides into a branch for the nerve above and one for 

 the nerve below. The anterior division of the first 

 (suboccipital) nerve grooves the atlas beneath the 

 vertebral artery, and joins the second, supplying the 

 rectus lateralis and recti antici muscles. It commu- 

 nicates with the sympathetic vagus, and hypoglossal 

 nerves. 



Its branches are superficial and deep. 



The superficial are divided into ascending and 

 descending. 



Ascending Branches. (a) The superficialis colli, 

 (b) auricularis magnus (great auricular), (c) occipital 

 minor. 



Descending Phrenic, from the third, fourth, and 

 fifth, descends on the scalenus anticus, then between 

 the subclavian artery and vein, and crosses the internal 

 mammary artery. It then crosses in front of the root 

 of the lung and runs between the pericardium and 

 mediastinal pleura to the diaphragm. 



THE BRACHIAL PLEXUS. The brachial plexus is 

 formed by the anterior divisions of the lower four 

 cervical and first thoracic, as follows: The fifth arid 

 sixth form an upper; the seventh, a middle; and the 

 eighth cervical with first dorsal a lower trunk. Each 

 of these trunks then separates into an anterior and a 

 posterior branch. 



