Till- CERVICAL I'l.KXUS 911 



CKHVICAI. Xi.in KS 



The anterior primary divisions of the upper four cervical nerves unite to form 

 the cervical plexus, and each receives a communicating branch from the superior 

 cervical sympathetic ganglion. The anterior divisions of the lower four cervical 



nerves arc joined by the greater part of the first ;horaci<- ner\e and they unite bo 

 form the brachial plexus (lit:--. (17"). <i~s, ti7!)). The til'th :,r,d sixth cervical nerves 

 receive communicating branches from the middle cervical sympathetic ganglion, 

 and the seventh and eighth from the inferior cervical ganglion, while the tirst thoracic 

 nerve is aKvays eonnected with the first thoracic sympathetic ganglion by a grey 

 ramus (figs. 117.") and 71S) anil in most case^ also by a white ramus comniunicans. 



THE CERVICAL I'LKXTS 



The cervical plexus (figs. <>7~> and 676) is formed by the anterior primary divisions 

 of the upper four cervical nerves which constitute the roots of the plexus. It lies 

 in the upper part of the side of the neck, under cover of the sterno-mastoid, and upon 

 the levator scapula- and the scalenus niedius. It is a loeped plexus, consisting of 

 three loops. The convexity of the upper loop is turned forwards, and the convexi- 

 ties of the lower two loops are directed backwards. 



As the anterior primary division of the first cervical nerve passes to the plexus 

 it runs outwards on the posterior arch of the atlas beneath the vertebral artery, 

 then it turns forwards, between the vertebral artery and the outer side of the upper 

 articular process of the atlas, and finally it descends, in front of the transverse 

 process of t IK; atlas, and unites with the upper branch of the second nerve, forming 

 with it the first loop of the plexus. It gives branches to the rectus capitis lateralis, 

 longus capitis (rectus capitis anterior major), and to the rectus capitis anterior 

 (minor). It communicates with the ganglion of the trunk of the vagus, with the 

 superior cervical ganglion of the sympathetic system, and by two branches with the 

 hypoglossal nerve (fig. 676). These communications with the latter form the 

 descendens hypoglossi and give the branches to the genio-hyoid and thyreo-hyoid 

 muscles. 



The second cervical nerve (anterior primary division) passes behind the upper 

 articular proce-s of the axis and the vertebral artery, and between the intertrans- 

 verse muscles extending from the first to the second cervical vertebrae, to the inter- 

 val between the scalenus medius and the longus capitis (rectus capitis anterior 

 major), where it, divides into two parts. The upper part ascends and unites with 

 the first nerve to form the first loop of the plexus, and the lower branch passes down- 

 wards and backwards and joins the upper branch of the third nerve in the second 

 loop of the plexus (figs. <>75, 676). It gives off the small occipital nerve and a fila- 

 ment to the sterno-mastoid, which communicates with the spinal accessory nerve in 

 the substance of the muscle, and it gives branches which assist in forming the ansa 

 hypoglossi, the cervical cutaneous, and the great auricular nerve (fig. 676). 



The third and fourth cervical nerves pass behind the vertebral artery (fig. 675) 

 and between the intertransverse muscles to the interval between the scalenus medius 

 and the longus capitis (rectus capitis anterior major), where the third unites with the 

 second and fourth nerves and completes the lower two loops of the plexus. The 

 anterior divisions of these nerves are about double the size of the preceding. The 

 third gives off a branch to the ansa hypoglossi, the larger part of the great auricular 

 and cervical cutaneous nerves, a branch to the phrenic, a branch to the supra-clavi- 

 cular nerves, and muscular branches to the scalenus medius. levator scapulae, longus 

 capitis, and trapexius (fig. 676). This last branch communicates with the spinal 

 accessory nerve beneath the muscle. The fourth nerve gives a branch to the phrenic. 

 a branch to the supra-clavicular nerves, and muscular branches to the scalenus 

 medius, levator scapula-, longus colli. and trapexius (fig. 676). The branch to the 

 trapexius unites with one from the third nerve and communicates with the spinal 

 accessory nerve beneath the muscle. 



Each root of the plexus receives a communicating grey ramus from the superior 

 cervical ganglion of the sympathetic, and from the roots and loops of the plexus a 

 number of branches arise which form two main groups, the superficial and the 

 deep. 



