442 GENERAL ARRANGEMENT OF NERVOUS SYSTEM. 



plies nerves of a special character to the mucous and muscular coats of 

 the pharynx, oesophagus, and stomach, and to those of the organs of 

 respiration in the neck and thorax. From the medulla oblongata and 

 the inferior or central parts of the brain, are also supplied the nerves 

 destined for the organs of special sense. 



In every region of the cerebro-spinal system, the two functions of 

 sensibility and motion are associated with each other by means of the 

 gray substance of the nervous centres. In the spinal cord the gray 

 substance is continuous and of nearly the same configuration through- 

 out. In the different parts of the brain it presents itself under the form 

 of more or less distinct deposits, of varying form and size. In either 

 of these parts a reflex action may take place independently of those 

 beyond, and calling into operation the special functions of the nervous 

 centre involved. But a nervous action may also pass through the entire 

 series, by the longitudinal connections of the cord, medulla oblongata, 

 tuber annulare, and cerebral ganglia, and thence through the radiating 

 fibres of the white substance to the cortical layer of the cerebral convo- 

 lutions. This layer may be regarded as a sort of concave mirror, where 

 the impressions coming from without are finally received and reflected, 

 in the form of conscious sensation and intelligent voluntary acts ; the 

 whole nervous mechanism of the cerebro-spinal system being thus called 

 into operation at the same time. 



