FUNCTIONS OF THE SPINAL CORD. 303 



display their customary phenomena. These effects are sometimes in- 

 structively witnessed in man when lesions of the cord have occurred 

 through disease. 



If the view that has been presented respecting the continuation of 

 fibres from the cord to the brain be correct, these fibres dis- ,, . 



1 Motor and sen- 



charge a commissural duty. This would lead us to sup- sory tracts of 



pose that there is a correspondence between the functions of { 

 the columns of the cord and those of the roots of the spinal nerves, the 

 anterior columns being motiferous, or in unison with the motor root of 

 the nerves, the posterior being sensiferous, or in unison with the sensory 

 root of the nerves. Agreeably to this, if the anterior columns be irri- 

 tated, motions are excited in all those parts which are supplied with 

 nerves beyond the irritated point ; and if the posterior columns be irri- 

 tated, in like manner pain is experienced. In this instance, however, a 

 certain amount of motion is occasionally observed, but this has common- 

 ly been explained by referring it to reflexion within the cord. It has 

 also been observed, as strengthening these views, that if the posterior 

 columns be irritated after complete section of the cord, the result will de- 

 pend on which of the cut portions be disturbed ; if it be the lower, there 

 will be no effect. An examination, under the same circumstances, of the 

 anterior columns, demonstrates that, if the upper section be irritated, there 

 is no effect produced ; if the lower, there are convulsive movements of 

 the parts supplied with nerves beyond. 



From these results we should infer that the physiological functions of 

 the anterior and posterior roots of the spinal nerves are participated in 

 by the anterior and posterior columns of the cord, and might therefore 

 expect that those functions would be continued in the higher distribu- 

 tion of the columns above the medulla oblongata. 



From the point of view under which we have thus presented it, the 

 action of the spinal cord is therefore simple, or it is disturb- General funo 

 ed by the agency of the brain ; in the first case it offers it- tions of the 

 self purely as an automatic instrument ; in the latter, its com- 

 missural connections with the brain make a compound apparatus. The 

 former state is closely represented in the construction of the amphioxus, 

 the nervous system of which has no rudiment of a cerebrum or cerebel- 

 lum ; in this animal, therefore, since also the sensory ganglia are merely 

 in a rudimentary state, the mode of life must be purely mechanical, just 

 as it is with an artificial automaton, of which, when a given spring is 

 touched, a given motion is made. Even among the highest vertebrated 

 animals, man himself at the periodic times of quiescence of the cerebrum, 

 as in sleep, when the cerebral influence over other portions is, to a certain 

 extent, suspended, an approach to a similar condition occurs ; but in 

 periods of activity of the cerebrum, it can hold the spinal cord in check, 



