494 NERVOUS SYSTEM* 



Of the Four Inferior Cervical Nerves. 



The trunks of these nerves, on issuing from the intervertebral 

 foramina, have one general mode of distribution, which permits 

 them to be described together or in common. 



The posterior branches are much smaller than those of the 

 preceding cervical nerves; they go backwards between the 

 complexus and the transverssriis colli, and leave filaments in 

 their passage with them; they then reach the splenius and the 

 trapezius, to which and to the integuments of the neck they are 

 distributed. 



The anterior branches are large; they appear on the side of 

 the neck, between the scalentis anticus and medius muscles ; 

 sometimes perforating the substance of one or the other of these 

 muscles. They each detach filaments to the sympathetic. The 

 fourth, also, commonly sends one to the phrenic. They then 

 form the Brachial Plexus. 



Of the Brachial Plexus and the Nerves of the Upper Extremity, 



The Brachial or the Axillary Plexus is formed by the junc- 

 tion and the intertexture of the four inferior cervical nerves, 

 and the first dorsal or thoracic. It extends from the scaleni 

 muscles to the axilla, on a level with the neck of the os humeri. 

 The nerves at first converge, and are situated somewhat be- 

 hind the subclavian artery where it passes over the first rib; 

 but are at various heights above it, according to their origin, 

 with the exception of the first dorsal nerve, which has to as- 

 cend in order to pass out of the thorax. 



The plexus is formed in the following manner. The fourth 

 and the fifth cervical nerves unite near the scaleni muscles into 

 a single trunk, which runs a short distance downwards, and 

 then splits into two. The seventh cervical and the first dorsal 

 do the same. The sixth cervical is the central nerve of the 

 plexus, and after going downwards two or three inches, it bifur- 

 cates also. Combinations of these primary divisions are formed, 

 which are dissolved, and then reformed, in such a way that a 

 thorough intertexture of the original nerves takes place. This 



