144 



Spinal Nerves. 



Comm.iff3v.ra 



media. 



Sulc. 

 longit. 



ad Gangl: 

 sympath. 



Ram,, post. 

 Ram. ant. 



488. Diagram of the Origins of the Spinal Nerves. 



The spinal nerves, Nervi spinales, are 31 pairs, and these are: 

 8 cervical, 12 dorsal, 5 lumbar, 5 sacral and 1 ^very rarely 2) coccy- 

 geal pairs. Each spinal nerve has two roots, an anterior, smaller, and a 

 posterior, larger ; they appear as flat fibrous bundles at the anterior 

 and posterior margins of the lateral tract, pass through the interverte- 

 bral foramen and unite to form a single rounded cord. The posterior 

 root only, is marked by a ganglion, the Ganglion intervertebralc, formed 

 in the intervertebral foramen. This root is sensory, the a n t e r i o r, motor. 

 The single cord formed by the two roots divides again, into an 

 anterior and a posterior division or branch, both of which 

 receive motor, as well as sensory fibres. The anterior larger division 

 communicates with the neighbouring sympathetic ganglion, and the neigh- 

 bouring anterior divisions of the spinal nerves, whereby loops, Ansae, 

 are formed, which are present everywhere except at the dorsal nerves, 

 where they are not constant. These ansae unite to form plexuses, 

 Plexus cervicalis , lumbaUs and sacralis. The posterior divisions, 

 irregularly united with the neighbouring branches, pass backwards to 

 the muscles and skin of the back ; they, however, supply only the long 

 muscles of the back, the broad muscles being supplied by nerves from 

 the plexus of the anterior divisions of the spinal nerves. 



