THE CERVICAL PLEXUS. 



1285 



Fig. 1086. 



The integument is therefore suppHed, from dorsal to ventral mid- line, by the 

 posterior primary division, the posterior and anterior divisions of the lateral 

 cutaneous branch and the anterior cutaneous branch of the anterior primary 

 division. The muscles derive their nerve-supply from both the anterior and the 

 posterior primary divisions. 



THE CERVICAL NERVES. 



The anterior primary divisions (rr. anteriores) of the eight cervical nerves (nn. 

 cervicales), assisted by the first and second thoracic, supply the head, neck, upper 

 extremity, thoracic integument and diaphragm. The first, second, third and 

 fourth communicate freely and form the cervical plexus for the supply of the head 

 and neck and the skin of the upper pectoral and shoulder regions, whilst the fifth, 

 sixth, seventh, and eighth, aided by the first and sometimes by the second thoracic, 

 form the brachial plexus, which supplies the upper extremity and the lateral 

 thoracic wall. 



THE CERVICAL PLEXUS. 



The cervical plexus (plexus cervicalis ) is formed by the union of the anterior 

 primary divisions (rr. anteriores) of the upper four cervical nerves (Fig. 1086). 

 After traversing the 

 intervertebral foramina, 

 they pass behind the 

 vertebral artery and 

 emerge, the first be- 

 tween the rectus capitis 

 lateralis and the rectus 

 capitis anticus minor 

 muscles, and the others 

 first between the inter- 

 transversales muscles 

 and then between the 

 rectus capitis anticus 

 major and scalenus me- 

 dius muscles. Each is 

 joined by a gray ramus 

 communicans, derived 

 either from the superior 

 cervical ganglion of the 

 sympathetic or from 

 the association cord be- 

 tween the superior and 

 middle cervical ganglia. 

 Under cover of the 

 sterno-mastoid the four 

 nerves are connected to 

 form the cervical plexus.- 

 The second, third and 

 fourth each divide into 

 an ascending and a 

 descending branch ; the 

 first does not divide. 

 These branches are connected in an irregular series of loops that constitute the 

 cervical plexus, which lies opposite the first four cervical vertebrae and upon the sca- 

 lenus medius and levator anguli scapulae muscles, and is covered by the sterno-mastoid. 



Branches. — The branches of the plexus may be divided into a S2iperficial and a 

 deep set. The former reach the under surface of the deep fascia at about the middle 

 of the posterior margin of the sterno-mastoid and are distributed to the integument 

 of the head, neck, shoulder and upper pectoral region. The latter are divided into 

 an internal and an external group, some of which supply the muscles of the neck 



Diagram illustrating plan of cervical plexus. 



