THE CERVICAL NERVES. 761 



of the atlas it receives a filament from the sympathetic. It then descends in front 

 of this process, to communicate with an ascending branch from the second cervi- 

 cal nerve. 



Communicating filaments from the loop between this nerve and the second 

 join the pneumogastric, the hypoglossal, and sympathetic and some branches are 

 distributed to the Rectus lateralis and the two Anterior recti. The fibres which 

 communicate with the hypoglossal simply pass through the latter nerve to become 

 for the most part the descendens hypoglossi. According to Valentin, the anterior 

 division of the suboccipital distributes filaments to the occipito-atlantal articula- 

 tion and mastoid process of the temporal bone. 



The anterior division of the second cervical nerve escapes from the spinal canal, 

 between the posterior arch of the atlas and the lamina of the axis, and, passing 

 forward on the outer side of the vertebral artery, divides in front of the Inter- 

 transverse muscle into an ascending branch, which joins the first cervical ; and 

 one or two descending branches, which join the third. It gives off the small 

 occipital ; a branch to assist in forming the great auricular ; another to assist in 

 forming the superficial cervical ; one of the communicantes hypoglossi, and a 

 filament to the Sterno-mastoid, which communicates in the substance of the 

 muscle with the spinal accessory. 



The anterior division of the third cervical nerve is double the size of the pre- 

 ceding. At its exit from the intervertebral foramen it passes downward and out- 

 ward beneath the Sterno-mastoid, and divides into two branches. The ascending 

 branch joins the anterior division of the second cervical ; the descending branch 

 passes down in front of the Scalenus anticus and communicates with the fourth. 

 It gives off the larger part of the great auricular and superficial cervical nerves ; 

 one of the communicantes hypoglossi ; a branch to the supraclavicular neVves ; a 

 filament to assist in forming the phrenic ; and muscular branches to the Levator 

 anguli scapulae and Trapezius ; this latter nerve communicates beneath the 

 muscle with the spinal accessory. Sometimes the nerve to the Scalenus medius 

 is derived from this source. 



The anterior division of the fourth cervical is of the same size as the preceding. 

 It receives a branch from the third, sends a communicating branch to the fifth 

 cervical, and, passing downward and outward, divides into numerous filaments, 

 which cross the posterior triangle of the neck, forming the supraclavicular nerves. 

 It gives a branch to the phrenic nerve, while it is contained in the intertransverse 

 space, and sometimes a branch to the Scalenus medius muscle. It also gives a 

 branch to the Levator anguli scapulae and to the Trapezius, which unites with the 

 branch given off from the third nerve, and communicates beneath the muscle with 

 the spinal accessory. 



The anterior divisions of the fifth, sixth, seventh, and eighth cervical nerves are 

 remarkable for their- size. They are much larger than the preceding nerves, and 

 are all of equal dimensions. They assist in the formation of the brachial plexus. 



The Cervical Plexus. 



The cervical plexus (Fig. 409) is formed by the anterior divisions of the. four 

 upper cervical nerves. It is situated opposite the four upper cervical vertebrae, 

 resting upon the Levator anguli scapulae and Scalenus medius muscles, and 

 covered in by the Sterno-mastoid. 



Its branches may be divided into two groups, superficial and deep, which may 

 be thus arranged : 



( Occipitalis minor. 

 ( Ascending . < Auricularis magnus. 

 ( Superficial colli. 



Superficial ^ 



( Suprasternal. 



(^Descending . Supraclavicular < Supraclavicular. 



( Siipra-acromial. 



