404 ANTERIOR CERVICAL NERVES. 



The Spinal nerves are divided into 



Cervical .... 8 pairs 



Dorsal .... 12 



Lumbar . . 5 



Sacral . .6 



The Cervical nerves pass off transversely from the spinal cord ; 

 the dorsal 'are oblique in their direction ; and the lumbar vertical, 

 and form the large assemblage of nerves at the termination of the 

 cord called cauda equina. 



The CERVICAL NERVES increase in size from above downwards ; 

 the first (sub-occipital) passes out of the spinal canal between the 

 occipital bone and the atlas ; and the last, between the last cervical 

 and first dorsal vertebra. Each nerve, at its escape from the inter-' 

 vertebral foramen, divides into an anterior and a posterior branch. 

 The anterior branches of the four upper cervical nerves form the 

 cervical plexus ; the posterior branches, the posterior cervical plexus. 



The anterior branches of the four inferior cervical together with 

 the first dorsal form the brachial plexus. 



Anterior cervical nerves. The Anterior branch of the first cervical 

 nerve escapes from the vertebral canal through the groove upon the 

 posterior arch of the atlas which supports the vertebral artery, 

 beneath which it lies. It then descends in front of the transverse 

 process of the atlas, and forms a loop by communicating with an 

 ascending branch of the second nerve. 



The Anterior branch of the second cervical nerve divides into three 

 branches at its exit from the inter vertebral foramen between the 

 atlas and axis, viz. an ascending branch, which completes the arch 

 of communication with the first nerve; and two descending branches, 

 which communicate with the third nerve. 



The Anterior branch of the third cervical nerve, double the size 

 of the preceding, divides at its exit from the intervertebral foramen 

 into numerous branches, some of which communicate and form 

 loops and anastomoses with the second, and others with the fourth 

 nerve. 



The Anterior branch of the fourth cervical nerve, of the same size 

 with the preceding, communicates by anastomosis with the third, 

 and sends a small branch downwards to the fifth nerve. Its prin- 

 cipal branches pass downwards and outwards across the posterior 

 triangle of the neck, towards the clavicle and acromion. 



The CERVICAL PLEXUS is constituted by the loops of communica- 

 tion, and by the anastomoses which take place between the anterior 

 branches of the four first cervical nerves. The plexus rests upon 

 the levator anguli scapula), posterior scalenus, and splenius muscle, 

 and is covered in by the sterno-mastoid and platysma. 



The branches of the cervical plexus may be arranged into three 

 groups, superficial ascending, superficial descending ; and deep 



