132 FUNCTIONS OF THE NERVOUS SYSTEM. 



the Posterior Pyramids are stated by Sir C. Bell to decussate^ like those of the 

 anterior ; they pass down chiefly into the posterior part of the middle column, 

 forming part also of the posterior. The fibres of the Restiform, or Cerebellar 

 columns, which, like those of the Olivary columns, do not decussate, mostly 

 pass downwards into the posterior columns ; but a band, (which has been 

 termed, from its curved aspect, the arciform layer) passes forwards into the 

 anterior columns. 



172. The following tabular view may assist, better than any delineations 

 could do, in the comprehension of this very intricate piece of Anatomy ; the 

 knowledge of which can be already applied to the explanation o/ many curious 

 pathological phenomena, and cannot but assist in. the elucidation of others 

 whose rationale is as yet obscure. 



SPIXAL CORD. MEDULLA OBLOXGATA. BIIAIX. 



I Arciform fibres of Cerebellar Columns ? Cerebellum 



Anterior Column < Olivary Columns - ... 5 Corpora Quadrigemina 

 f Non-decussating portion of Ant. Pyramids 7 p, 

 > Decussating portion of Ant. Pyramids J Cor P ora Stnata 



Middle Column 



Post. Pyramidal Columns (decussating) t 



5-> 



S Portion of Post. Pyramids (non-decus- > Thalami Optici 

 sating?) ) 



Restiform Columns Cerebellum 



VIII. Functions of the Spinal Cord. 



173. The functions of the Nervous System in Vertebrated Animals are so 

 complex in their nature, and our means of analyzing them are so imperfect, 

 that the inquiry is confessedly one of the greatest difficulty, and needs all the 

 light which can be thrown upon it from any source. The great accession to 

 our knowledge of them, which has been made within the last few years, 

 chiefly by the labours of Sir C. Bell and Dr. M. Hall, has so far changed the 

 aspect of this department of Physiological Science, as to render it necessary 

 for those who had previously studied it, to begin de novo. This is especially 

 the case in regard to the actions dependent on the Spinal Cord ; which it 

 seems desirable to consider in the first instance, in order that it may be clearly 

 defined what the Brain does not do. By many, even in recent times, the 

 Spinal Cord has been considered as a mere appendage to the Brain ; but the 

 phenomena of its independent action render such an idea quite inadmissible. 

 These phenomena have been especially pointed out by Dr. M. Hall; and it 

 is mainly owing to his arguments, that Physiologists are now for the most 

 part agreed in the general fact, that the Spinal Cord constitutes a distinct 

 centre, or rather a collection of centres, of nervous influence, and that its ope- 

 rations are carried on through the nervous trunks with which it is connected. 

 It is further generally admitted that its functions are independent of the will ; 

 and that they are in effect frequently opposed to those of the brain, which 

 operates on the muscles either by a volitional or by an emotional impulse. 

 And, lastly, its actions are-always (except when excited by a physical irrita- 

 tion directly applied to itself) entirely of a reflex character: that is to say, 

 the motor impulses which originate in it are not spontaneous, but result from 

 the stimulus of impressions, conveyed to it by the afferent trunks, and ope- 

 rating upon it, to use the expression of Prochaska, according to certain "pecu- 

 liar laws written, as it were, by nature on its medullary pulp." It is not, 

 however, universally admitted that these actions are independent of sensation; 

 and some eminent physiologists, among whom may be named Dr. Alison, still 

 hold that the intervention of sensation is necessary, in the case at least, of 

 the ordinary associated movements, which have definite ends in view, and 



