178 



THE NERVOUS SYSTEM. 



Fig. 1 1 8 



smallest. The ganglion is not attached to the dorsal root alone 

 but is prolonged a short distance beyond the point of union of the 

 two roots ; this is best seen in the nerves of the lumbar plexus. 



Each ganglion is a yel- 

 lowish-white rounded 

 or oval body, with an 

 outer thick (sometimes 

 o - i5 mm. thick) sheath 

 of connective - tissue, 

 connected by the epi- 

 neurium of the nerve 

 roots with the Dura 

 mater. This sheath is 

 composed of bundles of 

 parallel, wavy, white, 

 connective-tissue fibres, 

 - which enclose a large 

 number of connective- 

 tissue corpuscles, and 

 here and there contains 

 brown pigment. 



By means of longi- 

 tudinal and transverse 

 sections it may be seen 

 that the ganglion sur- 

 rounds the ventral root, 

 but that it forms a 

 thinner layer on that 

 side, where the dorsal 

 root joins the ventral ; 

 although at this point 

 the two roots and the 

 ganglion are firmly uni- 

 ted together, the thick 

 fibrous sheath of the 

 ganglion prevents any 

 communication be- 



Ventral view of the brain and spinal cord, to show the tween the nei'VOUS de- 



points of exit of the spinal nerves. 



ments ot the ventral 



MI-IO Spinal nerves. 



VG Trigeminal ganglion. root and tllOSe of the 



Wi-io Vertebrae. ,. 



XG Ganglion of vagus. ganglion. 



