FUNCTIONS OF THE SPINAL CORD. 633 



opposite side, others running upwards and downwards for the space of half 

 an inch or more in the posterior columns before decussating ; and that, having 

 decussate <1, these fibres run from below upwards in the gray substance of the 

 cord. 2. That the motor nerves run for the most part in the anterior and 

 antero-lateral columns, and that they decussate at the lower part of the 

 medulla oblongata. 3. That there are special conductors for particular 

 sensations as for touch, paiu, tickling, and temperature, which decussate 

 in the cord, whilst there are others, viz., those which convey motor impulses 

 to the muscles, and to the vessels, as well as those ministering to the muscular 

 sense, which do not decussate. 



502. The Cord as an Independent Centre. We have now to consider the 

 Spinal Cord as an independent centre of nervous power, and to inquire 

 whether the movements which are excited through its "reflex" activity 

 necessarily involve sensation. These movements are most characteristically 

 displayed, when the Spinal Cord is cut off from communication with the 

 higher Nervous centres; probably rather because the nerve-force excited by 

 the impression reacts through the Spinal ganglion to which it is conveyed, 

 when it can no longer pass on to the Encephalic centres ( 459), than be- 

 cause (as some suppose) the impulse to reflex movement is ordinarily neu- 

 tralized and rendered inoperative by an effort of the Will. It is true that 

 those reflex actions of the Spinal Cord, which are necessary to the mainte- 

 nance of Organic life, and which are equally performed whether the Spinal 

 axis be in communication with the higher Encephalic centres or not, are 

 continually modified or temporarily suspended by the Will; but this is only 

 when we consciously bring the Will to bear upon them; and it is no less 

 certain that we are not continually making any such exertions, in order to 

 antagonize movements, which (as we learn from Pathological evidence 1 ) 

 would be continually excited but for this neutralizing influence, if such a 

 doctrine were correct. The readiest demonstration of the independent power 

 of the Spinal Cord, is derived from the motions exhibited by the limbs of 

 animals, when irritation is applied to them after section of the Spinal Cord 

 at some point above the entrance of their nerves ; the fact that these move- 

 ments are reflected through the Cord, and are not the product of direct 

 stimulation applied to the part irritated, being shown by their complete, 

 cessation when the nerve-trunks are divided, or the substance of the Spinal 

 Cord is broken down. Thus, if a frog be decapitated, its body remains sup- 

 ported on its limbs in the usual position, and will recover this if it be dis- 

 turbed ; irritation of the feet will cause it to leap ; and tickling the cloaca 

 with a probe will excite efforts to push away the instrument. 2 It is to be 



1 See, for example, the case of Softening of the Spinal Marrow, recorded by Dr. 

 Nairne in the Med.-Chir. Trans., vol. xxxiv; in which a portion of the Cord at 

 least an inch long, situated opposite the third and fourth dorsal vertebrae, was " so 

 soft that the slightest pressure of the finger broke it up," being nearly in a fluid state 

 through its whole thickness ; yet the patient felt pain in his lower limbs, showing 

 that the power of upward transmission remained ; and although he had lost all Volun- 

 tary control over the muscles of the lower part of the body, yet they were affected 

 with incessant choreie movement (which, according to Dr. Hughlings Jackson, Edin. 

 Med. Journ., Oct. 1868, p. '294, originates in embolism of the vessels of the Sensory 

 Ganglia), and these movements were affected in such a marked manner by emotions, 

 as plainly to indicate a downward transmission of motor power. 



2 It has been pointed out by Messrs. Todd and Bowman (Physiological Anatomy, 

 vol. i, p. 315), that the Spinal Cord of the male trog, at the season of copulation, 

 naturally possesses a state of most extraordinary excitability. The thumb of each 

 anterior extremity at this season becomes considerably enlarged, as is well known to 

 Naturalists. "This enlargement is caused principally by a considerable development 

 of the papillary structure of the skin which covers it; so that large papillae are 

 formed all over it. A male frog, at this season, has an irresistible propensity to 



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