100U 



THE NERVOUS SYSTEM 



different distances away from the vertebral column' (1) A large portion of the cells 

 remain near the central system and form a linear series of ganglia which, with the 

 trunks connecting them, become two gangliated nerve-cords extending along each side, 

 proximal to and parallel with the vertebral column; (2) a still larger portion of the 

 cells migrate further towards the periphery and are accumulated into ganglia which 

 assume an intermediate position and which, with the rami connecting them with each 

 other and with other structures, fortn a series of great prevertebral plexuses; (3) still 

 other cells wander even further away from the locality of their origin and invade the 

 very walls of the organs innervated by the sympathetic system. The latter cells 

 occur as numerous small terminal ganglia, most of which are microscopic and which, 

 with the twigs connecting them, form the most peripheral of the sympathetic plexuses. 

 Examples of these are the intrinsic ganglia of the heart and pancreas and the plexuses 

 of Auerbach and Meissner in the walls of the digestive canal. Small, straggling 



FIG. 717. SCHEME SHOWING THE CONNECTION BETWEEN THE SYMPATHETIC AND THE CEREBRO- 



SPINAL AND CENTRAL NERVOUS SYSTEMS. 

 AS, Afferent sympathetic fibres; D, Dogiel spinal ganglion-cell of type II. 



--- GREY RAMUS 



COMMUNICANS 

 WHITE RAMUS 

 COMMUNICANS 



VENTRAL ROOT 



GANGLI- 

 ATED 

 CORD 



--. POSTERIOR PR I- 

 MA K Y DIVISION 

 AKTKK1OR PRI- 

 MARY DIVISION 



-. AFFERENT SPLAX- 



CH\I(< FIBRE 

 - EFFERENT SPLAN- 

 ^ 1'IIMi' FIBRE 



- GREY RASTCS 



COMMUNICANS 

 WHITE RAHI'X 

 COStMUfflCAKS 



BRANCH TO PREYERTEHRM. 

 SYMPATHETIC GANGLION 



ganglia may be found scattered between these three general groups. The supporting 

 tissue of the sympathetic system accumulates early and is probably all of mesodermic 

 origin. 



Construction of the sympathetic system. The sympathetic ganglia may be 

 considered as relays in the pathways for the transmission of impulses from the region 

 in which they arise to the tissues in which they are distributed; the cells composing 

 the ganglia are the cell-bodies of the neurones interposed in the various neurone 

 chains performing this function. A fibre arising from a cell-body in a given ganglion 

 may pass out of the ganglion and proceed directly to its termination upon a smooth 

 muscle-fibre or gland-cell, or it may pass through a connecting trunk to another 

 ganglion and there terminate about and thus transmit the impulse to another cell, 

 which, in its turn, may give off the fibre which bears the impulse to the appropriate 

 tissue-element. Fibres arising in given ganglia may pass through other ganglia and 

 proceed uninterrupted to their respective destinations. On the other hand several 



