344 INNERVATION. [cHAP.Xl. 



reason to believe that the will exerts a primary influence upon either 

 or both of these gangliform bodies, more vigorous when aided 

 and guided by the power of the cerebral hemispheres. The fre- 

 quent paralysis of motion apart from sensation, when the upward 

 continuations of the pyramidal fibres in the corpora striata are 

 diseased, renders it extremely probable that these fibres are the me- 

 dia of connexion between the brain and cord in voluntary actions. 



The medulla oblongata is not less the medium for the transmis- 

 sion of sensitive impressions from all the regions of the head, trunk, 

 and extremities ; and from its olivary columns at their upper and 

 posterior part being, as it were, the concourse of all the nerves of 

 pure sense, it seems fair to assign these parts as the prime seat 

 of those central impressions which are necessary for sensation. The 

 reception of these impressions by the cerebral hemispheres is the 

 stage immediately associated with mental perception. True sen- 

 sation, therefore, cannot take place without cerebral hemispheres. 

 In a sensation excited in parts supplied by spinal nerves, the first 

 central change is probably in the posterior horn of the vesicular 

 matter of the cord; and the olivary column of the medulla 

 oblongata is simultaneously affected, from its connexion with 

 the cord. The change in this latter part is then propagated to 

 the cerebral hemispheres. 



Thus much is suggested by anatomy, as regards the mechanism 

 of sensitive impressions. Experiment affords us no aid in this 

 intricate and difficult subject; neither does pathological ana- 

 tomy : for the parts are so closely associated with each other, 

 that any morbid state of one readily involves the others, so that 

 it is almost impossible to find a morbid state of the parts devoted 

 to sensation, apart from an affection of those more immediately 

 concerned in motion. 



The function of the restiform bodies is probably associated with 

 that of the hemispheres of the cerebellum, and of the posterior 

 columns of the spinal cord. 



The experiments of Le Gallois and Flourens render it certain 

 that the medulla oblongata is the centre of respiratory movements. 

 The latter physiologist assigns as the " primum movens " of these 

 acts all that portion of the medulla which extends from the fila- 

 ments of origin of the vagus nerve to the tubercula quadrigemina, 

 the former only inclusive. Destruction of this portion, in whole or 

 in part, invariably impairs or destroys the respiratory actions, and 

 a morbid state of it gives rise to irregular or excited movements of 

 respiration. Sighing, yawning, coughing, are probably connected 



