374 FUNCTIONS OF SPINAL COED : EEFLEX ACTION. 



463. We shall now consider, in more detail, the functions 

 of the different parts of the Cerebro-Spinal System in Man 

 and the higher animals ; referring occasionally to the Inver- 

 tebrated classes for illustrations which they can best afford. 

 We shall commence by examining the functions of the Spinal 

 Cord and Medulla Oblongata, which are the parts concerned 

 in reflex action. 



Functions of the Sjiinal Cord. Reflex Action. 



464. The Spinal Cord of Vertebrated Animals may be con- 

 sidered as a collection of ganglia, analogous to those of which 

 the ganglionic cord of Articulata is composed ; these ganglia 

 being united, however, in an unbroken line, instead of being 

 distinct from one another and brought into communication by 

 coiinecting cords. There is great difficulty in tracing-out the 

 precise course of the nerve-fibres which form the white strands 

 of the Spinal Cord ; and it is doubtful how far any of them 

 form a continuous connexion between the roots of the Spinal 

 Serves and the Brain. But there can be no doubt that such 

 a connexion is established, either by the fibrous tracts or by 

 the grey matter of the Spinal Cord; experiment having 

 unequivocally shown that the latter participates with the 

 former in this conducting power. 



465. When the Cerebro-Spinal system is in full activity, 

 its nerves convey impressions from every part of the body to 

 the Brain, where they are communicated to the mind, that is, 

 the individual becomes conscious of them, or feels them as 

 sensations. And by the fibres of the same system which pass 

 in the contrary direction, the will acts upon the muscles so as 

 to produce voluntary motion. Now the brain is not in con- 

 stant action, even in a healthy person ; it requires rest ; and 

 during profound sleep it is in a state of complete torpor. Yet 

 we still see those movements continuing, which are essential 

 to the maintenance of life ; the breathing goes on uninter- 

 ruptedly, liquid poured into the mouth is swallowed, and the 

 position is changed when the body would be injured by 

 remaining in it. The same is the case in apoplexy, in which 

 the actions of the brain are suspended by pressure upon it. 

 And the same will take place, also, in an animal from which 

 the cerebrum has been removed ; or in which its functions 

 are completely suspended by a severe blow on the head. If 



