THE NERVOUS SYSTEM. 



I. THE CENTRAL NERVOUS SYSTEM. 





ORIGINALLY WRITTEN BY D. J. CUNNINGHAM, F.E.S., 



Late Professor of Anatomy, University of Edinburgh ; 



EEVISED AND PARTLY REWRITTEN BY G. ELLIOT SMITH, F.B.S., 



Professor of Anatomy, University of Manchester. 



In its original form this chapter represented perhaps the most characteristic work of the late Editor 

 of this Text-book, which continues to bear his name, and is a lasting memorial of his personality 

 d scientific attainments. By his lamented death the difficult task has fallen upon the reviser 

 making such considerable alterations as the rapid changes in the state of our knowledge of the 

 ervous system have rendered unavoidable, while endeavouring at the same time to 

 naltered the general character of his friend's work.] 



ELEMENTS OF THE CENTEAL NEEVOUS SYSTEM. 



tegumentary 



peripheral process 

 --sensory nerve cell 



central 



process 



IY type of nervous system with which we are acquainted, from the simplest 

 ind most primitive, such as that of Hydra, to the most complex and highly 

 daborated mechanism p A 



, . . >" * rpniim*>nrnr\/ -f^~ 



ound in man, is com- 

 )osed essentially of 

 -hree categories of 

 Cements. These are 

 1) sensory cells, so 

 ituated and so special- 

 :sed in structure as to 

 ')e capable of being 

 Affected by changes in 

 he animal's environ- 

 ment, and of transmit- 

 ing the effects of such 

 Simulation, directly or 

 ndirectly, to (2) effer- 

 ent nerve-cells, which 

 nfluence the muscles 

 >r other active tissues, 

 o that the stimulation 

 'nay find expression in 

 ome appropriate action; 

 nd (3) intercalated 

 lerve-cells, which regu- 

 ate such responsive be- 

 laviour by bringing it 

 mder the influence of other sensory impressions and of the state and activities of 

 he body as a whole. 



497 33 



i nte real ate di 

 nerve cells 



muscle 



FIG. 439. A DIAGRAM REPRESENTING THE ESSENTIAL FEATURES IN THE 

 ARRANGEMENT OF THE MOST PRIMITIVE TYPE OF NERVOUS SYSTEM. 



