NERVE PLEXUSES 



285 



the neck and trunk, and to the upper and lower extremities. 1 

 In all regions except the thoracic, the anterior divisions interlace 

 with each other to form plexuses before giving off nerves. 

 A nerve plexus is a network formed by 

 branches of several main nerves which have 

 different central connections. (See p. 296.) 

 From the plexus other nerves proceed to 

 their separate distributions. 



A nerve made up of fibers which have 

 been part of a plexus conveys impulses to 

 or from several different parts of the spinal 

 cord. 



The most important plexuses are: 



The cervical plexus (formed by the upper four 

 cervical nerves). 



The brachial plexus (formed by the lower four 

 cervical and first thoracic nerves). 



The lumbar plexus (formed by the upper three 

 and part of the fourth lumbar nerves). 



The sacral plexus (formed by the lower lum- 

 bar, and upper three and most of fourth sacral 

 nerves). 



The larger nerves only are described in the 

 text. Resumes are added for reference. 



For nerves supplying the joints see page 74. 



FIG. 1 80. CAUDA EQUINA. 

 (Morris.) 



FIG. 181. SHOWING DIVISION OF 

 NERVE. 



i, Dura mater; 2, arachnoid; 3, 

 ganglion of post, root; 4, ant. root; 5, 

 space containing spinal fluid; 6, post, 

 division of nerve. (Holden.) 



1 The communicating branches to sympathetic ganglia are of great importance, 

 serving to connect the cerebro-spinal and sympathetic division into one great nerve 

 system. (They are the white rami communicanles.) 



