378 REFLEX ACTIONS OF THE SPINAL CORD. 



pneumogastric. If the trunk of the glosso-pharyngeal nerve 

 be pinched, an act of deglutition is made to take place ; but 

 if it be separated from the Medulla Oblongata, or the pneumo- 

 gastric nerve be divided, or the Medulla Oblongata itself be 

 destroyed, the movement can no longer be thus excited. 

 Hence we see the necessity of the completeness of this 

 nervous chain or circle consisting of the nerve proceeding 

 from the part stimulated to the ganglion, the ganglion itself, 

 and the nerve proceeding from the ganglion to the muscles 

 acted-on in order that any such reflex movements may be 

 produced. 



471. The functions of the Spinal Cord appear to be wholly 

 restricted to the performance of movements of this character. 

 The proportion they bear to the motions which are de- 

 pendent upon sensation and will, varies greatly in different 

 animals ; and it may be judged-of with tolerable accuracy, by 

 comparing the relative sizes of the spinal cord and the brain. 

 Thus in the lowest Fishes, the spinal cord seems the principal 

 organ, and the brain an insignificant appendage to it. In 

 Man, on the contrary, the spinal cord is so small in com- 

 parison with the brain, as to have been regarded (though 

 incorrectly, as we have seen) in the light of a mere bundle 

 of nerves proceeding from it. In the former, the ordinary 

 movements of the body seem principally to depend upon the 

 spinal cord, being only controlled and directed by the brain ; 

 just as those of Articulated animals are chiefly dependent 

 upon the ganglia of the trunk, being only guided by those of . 

 the head ( 442). But in Man, those only are left to the 

 spinal cord which are necessary for the maintenance of life ; 

 the ordinary motions of the body being for the most part 

 voluntary. Still, as we have just now seen ( 468), reflex 

 movements may be excited through the spinal cord, even in 

 Man, when the influence of the will is cut off; and it is 

 curious to observe, that the stimulus is most powerful when 

 it acts upon the soles of the feet, and that it ceases to produce 

 the same effect, when, by the restoration of the functions of 

 the injured part of the cord, the power of the will over the 

 limbs, and also their sensibility, are regained. There is much 

 reason to believe that, when we are walking steadily onwards, 

 and the mind is intently occupied with some train of thought 

 which engrosses its whole attention, the individual movements 



