630 



THE SPINAL NERVES. 



THE ROOTS OF THE SPINAL NERVES. 



Each spinal nerve springs from the spinal cord by two roots which 

 approach one another, and, as they quit the spinal canal, join in the 

 corresponding intervertebral foramen into a single cord ; and each cord so 

 formed separates immediately into two divisions one of which is destined 

 for parts in front of the spine, the other for parts behind it. 



The posterior roots of the nerves are distinguished from the anterior roots 

 by their greater size, as well as by the greater thickness of the fasciculi of 

 which they are composed. Each spinal nerve is furnished with a ganglion ; 

 but the first cervical or sub-occipital nerve is in some cases without one. 

 The size of the ganglia is in proportion to that of the nerves on which they 

 are formed. 



The ganglia are in general placed in the intervertebral foramina, imme- 

 diately beyond the points at which the roots perforate the dura mater lining 

 the spinal canal. The first and second cervical nerves, however, which 

 leave the spinal canal, over the laminae of the vertebrae, have their ganglia 

 opposite those parts. The ganglia of the sacral nerves are contained in the 

 spinal canal, that of the last nerve being occasionally at some distance from 

 the point at which the nerve issues. The ganglion of the coccygeal nerve 

 is placed within the canal in the sac of dura mater, and at a variable dis- 

 tance from the origin of the nerve. 



Fig. 421. Fig. 421. DIFFERKS-T 



VIEWS OF A PORTION OP 

 THE SPINAL CORD FROM 

 THK CERVICAL REGION 

 WITH THE ROOTS OF 

 THE NERVES. Slightly 

 enlarged. 



In A, the anterior sur- 

 face of the specimen is 

 shown, the anterior nerve- 

 root of the right side 

 being divided ; in I>, a 

 view of the right side is 

 given ; in C, tho upper 

 surface is shown ; in D, 

 the nerve-roots and gan- 

 glion are shown from 

 below. 1, the anterior 

 median fissure ; 2, pos- 

 terior median fissure ; 3, 

 anterior lateral depres- 

 sion, over which thu ante- 

 rior nerve-roots are seen 

 to spread ; 4, posterior 

 lateral groove, into which 

 the posterior roots are 

 seen to sink ; 5, anterior 

 roots passing the ganglion ; 

 5', in A, the anterior root 

 divided ; 6, the posterior roots, the fibres of which enter the ganglion, 6' ; 7, the uciled 

 or compound nerve ; 7', the posterior primary branch seen in A and D, to be derived in 

 part from the anterior and in part from the posterior root. 

 



The fibres of the po: terior root of the nerve divide into two bundles as they 

 approach the ganglion, and the inner extremity of the oval-shaped ganglion 

 is sometimes bilobate, the lobes corresponding to the two bundles of fibres. 



