CHAP. XI.] PHYSICAL ACTIONS OF THE CORD. 339 



brain is the part primarily affected, the mental impulse is at the 

 same time directed to that portion of the cord upon which the 

 required action depends. 



In the development of sensation the stimulus affects the posterior 

 horns of the gray matter of the cord, which, from its commissural 

 connexion with the brain, is in reality a part of the sensorium. 

 When the power of mental interference is removed, or kept under 

 control, physical actions develop themselves ; being affected through 

 the same nerves as those which volition influences, or which sensi- 

 tive impressions affect. The latter are, in such instances, the 

 exciters of the former, no doubt through the vesicular matter in 

 they are implanted. These actions become most manifest 

 the connexion of the brain with the spinal cord has been 

 ivered ; and they occur in the most marked way in those situations 

 ^here the cutaneous nerves are so organized as readily to respond 

 the application of a stimulus applied to the surface, or they 

 icome universal when the cord is in a state of general excite- 

 icnt. 



The movements in locomotion and the maintenance of the various 

 ittitudes, are affected through the ordinary channels of the physical 

 md volitional actions ; and the posterior columns of the cord, by 

 icir influence on the vesicular matter of the segments in which 

 nerves are implanted, co-ordinate and harmonize the compli- 

 ited muscular actions of the limbs and the trunk under the QOII- 

 )1 of that portion of the encephalon which probably is devoted to 

 lat purpose. This power of co-ordination is probably mental, and 

 intimately connected with the muscular sense. 

 To conclude the discussion of the functions of the cord, we shall 

 enumerate the physical nervous actions of which it is the 

 mtre, remarking, at the same time, that we continue to use the 

 jrm spinal cord in its ordinary sense, and that we reject the hypo- 

 thesis of a true spinal cord, anatomically distinct from that which 

 has to do with mental nervous actions. 



We have already stated, that probably part of the muscular 

 adjustments in locomotion are excited by the pressure against the 

 soles of the feet. All involuntary movements of the muscles of the 

 trunk or extremities, when excited by external stimuli, have their 

 centre in the spinal cord. The sudden application of cold to the 

 surface of the trunk or extremities, frequently excites respiratory 

 movements. This may be attributed to cutaneous nerves affecting 

 the gray matter of the cord, and through this the intercostal and 

 phrenic nerves implanted in it. 



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