NERVOUS SYSTEMS, PERIPHERAL AND CENTRAL 487 



The cerebral ganglion, or brain, is developed in the anterior end, or head, 

 of an animal in connection with the formation of the elaborate system of the 

 " distance receptors," which enable the organism to take account of occurrences 

 not in immediate contact with it. 



The reactions of the highest part, the cortex cerebri, show, in contradistinction 

 to the reflexes of the spinal cord, much greater possibilities of modification by 

 events elsewhere and by previous activity. Inhibitory phenomena are especially 

 noticeable and the power of changing excitation into inhibition, and vice versa, is 

 a characteristic function of the cortex. Other properties are discussed in the text. 



Certain aspects of the formation of new associations, or " memory," are also 

 discussed in the text. 



The sympathetic system, as well as the autonomic or visceral system in general, 

 is not an independent nervous system, but an outflow or outflows of efferent 

 fibres from particular regions of the central nervous system. Its characteristic is 

 the presence of synapses with secondary neurones, either in the sympathetic chain, 

 or more peripherally ; the axones of these second neurones are non-medullated. 

 The visceral system develops by outgrowths of chains of cells, whereas the somatic 

 system is formed by outgrowth of axones from cells in the centres. 



Auerbach's plexus, although endowed with reflex functions, is also developed 

 as an outgrowth from the central nervous system and cannot be regarded as 

 survival of a primitive peripheral nervous system. 



LITERATURE 



General. 



Bethe (1903). Sherrington (1906). Starling (1912, pp. 324-632). 



Washburri (1909). 



Origin. 



Parker (1909, 1911). 



Properties of the Neurone. 



Ross Harrison (1910). Mott (1912). 



Nerve Networks. 



Hofmann (1907). 



Cerebral Cortex. 



Graham Brown and Sherrington (1912). Mott (1910). 



Speech. 



Mott (1910). 



Sympathetic and Visceral System. 

 Gaskell (1886-1889). 



