722K 



PHYSIOLOGY OF THE NERVOUS SYSTEM. 



the medulla on either side would affect the 

 same side of the body, no decussation existing 

 between the fibres of opposite restiform or pos- 

 terior pyramidal bodies. The irritating or de- 

 pressing influence of the lesion would probably 

 be extended to the spinal grey matter of the 

 same side. 



That the medulla oblongata is the channel 

 through which the operations of the brain are 

 associated in voluntary actions with the spinal 

 cord, is shewn by the fact that paralysis of all 

 the muscles of the trunk follows the separation 

 of the latter organ from the former. It seems 

 not improbable that the centre of volition is 

 connected with one of the gangliform bodies 

 in which the columns of the medulla oblon- 

 gata terminate above (the corpora striata), so 

 that the column connected with each corpus 

 striatum (the anterior pyramid) is well placed 

 for conveying voluntary impulses downwards. 

 When the cerebral hemispheres have been 

 removed, as in Flourens' and in Magendie's 

 experiments, the bird is thrown into a deep 

 sleep, a state of stupefaction, and insensibility 

 to surrounding objects. But as he can main- 

 tain his attitude, stand, walk when first pro- 

 pelled, fly if thrown into the air, it may be 

 inferred that some degree at least of mental 

 or volitional effort remains. Some of the ani- 

 mal's movements have the appearance of the 

 exercise of will, although, doubtless, many of 

 them are in a great degree excited by physical 

 stimuli. I may instance, in particular, what I 

 have noticed in my own repetition of Flourens' 

 experiments, a peculiar movement of the head, 

 as if the bird were trying to shake off some 

 object which irritated the head, and a frequent 

 opening and shutting the bill, with movements 

 of deglutition. Hence there seems reason to 

 believe that the will may be exercised inde- 

 pendently of the cerebral convolutions and 

 their fibres, and that, under all circumstances, 

 it 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 frequent paralysis 

 of motion apart from sensation, when the up- 

 ward continuations of the pyramidal fibres in 

 the corpora striata are diseased, renders it ex- 

 tremely probable that these fibres are the media 

 of connection between the brain and cord in 

 voluntary actions. 



The medulla oblongata is also the medium for 

 the transmission of sensitive impressions from 

 all the regions of the head, trunk, and extremi- 

 ties; and from its olivary columns at their upper 

 and posterior part in the mesocepbale 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. Perfect sensation, 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 

 connection with the cord. The change in this 

 latter part is then propagated to the cerebral 

 hemispheres. 



Thus much is suggested by anatomy, as re- 

 gards the share which the medulla oblongata 

 takes in the mechanism of sensitive impressions. 

 Experiment affords us no aid in this intricate 

 and difficult subject ; neither does pathological 

 anatomy : 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 pro- 

 bably 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 

 make it certain that the medulla oblongata is 

 the centre of respiratory movements. The lat- 

 ter physiologist assigns as the " primum mo- 

 vens " of these acts all that portion of the me- 

 dulla which extends from the filaments of origin 

 of the vagus nerve to the tubercula quadrige- 

 mina, 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 with 

 excitation of this centre, either direct, or propa- 

 gated to it from some sentient surface. It 

 seems not improbable that a portion of the 

 spinal cord as low down as the spinal acces- 

 sory nerve goes, is associated with this centre 

 in the respiratory movements. 



This portion of the encephalon is also the 

 centre of action in the movements of degluti- 

 tion, through fibres of the glosso-pharyngeal 

 and vagi nerves. A morbid state of it occasions 

 difficulty, or even paralysis, of deglutition. 

 Animals deprived of the cerebral hemispheres 

 and cerebellum will preserve the power of 

 swallowing food introduced within the grasp 

 of the fauces, so long as the medulla oblongata 

 continues uninjured. In foetuses born without 

 cerebral hemispheres, those actions are present 

 which depend on the spinal cord and medulla 

 oblongata ; all the movements of respiration 

 and deglutition are performed as well as in the 

 perfect foetus. Mr. Grainger's experiments 

 shew that puppies deprived of the hemispheres 

 of the brain can perform the movements of 

 suction with considerable vigour, when the 

 finger is introduced into the mouth ;* and the 

 remarkable fact of the adhesion of the foetus of 

 the kangaroo to the nipple within the pouch, 

 no less than its respiratory movements, must, as 

 this author remarks, be regarded as a most in- 

 teresting display of the physical power of the 

 medulla oblongata, while the rest of the brain is 

 as yet undeveloped. 



The actions of respiration and pharyngeal 



* Loc. cit. pp. 80-1. 



