500 THE NERVOUS SYSTEM. 



radiations of impressions, there are, perhaps, no means 

 of deciding whether they take place in the spinal cord or 

 in the brain ; but the analogy of the cases of transference 

 makes it probable that the communication is, in this also, 

 effected in the cord. 



The power, as a nerve-centre, of communicating im- 

 pressions from sensitive to motor, or, more strictly, from 

 centripetal to centrifugal nerve-fibres, is what is usually 

 discussed as the reflex function of the spinal cord. Its 

 general mode of action, its general though incomplete 

 independence of consciousness and of the will, and the- 

 conditions necessary for its perfection, have been already 

 stated. These points, and the extent to which the power 

 operates in the production of the natural reflex movements- 

 of the body, have now to be further illustrated. They 

 will be described in terms adapted to the general rules of 

 reflection of impressions in nervous centres, avoiding all 

 such terms as might seem to imply that the power of the 

 spinal cord in reflecting, is different in kind from that of 

 all other nervous centres. 



The occurrence of movements under the influence of the 

 spinal cord, and independent of the will, is well exemplified 

 in the acts of swallowing, in which a portion of food, 

 carried by voluntary efforts into the fauces, is conveyed by 

 successive involuntary contractions of the constrictors of 

 the pharynx and muscular walls of the oesophagus into 

 the stomach. These contractions are excited by the stimu- 

 lus of the food on the centripetal nerves of the pharynx 

 and oesophagus being first conducted to the spinal cord 

 and medulla oblongata, and thence reflected through the 

 motor nerves of these parts. All these movements of the 

 pharynx and oesophagus are involuntary; the will cannot 

 arrest them or modify them ; and though the mind has a 

 certain consciousness of the food passing, which becomes 

 less as the food passes further, yet that this is not neces- 

 sary to the act of deglutition, is shown by its occurring 



