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 downsvards. NVhen the cerebral hemispheres have been removed, as in Flourens' and in Alagendie'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. Bence 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 poser 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 tmnsmission 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 inesocephale 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 im_pressions 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 svithout 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 " primurn mo yens " of these acts all that portion of the me dulla which extends from the filaments oforigin 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-pharyugeal 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 svvallowing food introduced within the grasp of the fauces, so long as the medulla oblongata continues uninjured. In ketoses 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 fcetus. Air. Grainger's experiments shew that puppies deprived of the hemispheres of the brain can perform the movements ofi suction with considerable vigour, when the finger is introduced into the mouth ;11 and the remarkable fact of the adhesion of the fcetus 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 rnedulla oblongata, while the rest of the braiu is as yet undeveloped.
The actions of respiration and pharyngeal _ deglutition are, to a great extent, of the physi cal kind, being excited by impressions propa gated from the periphery. In those of respira tion, the ordinary excitin,,o. cause is probably, as Dr. Hall suggested, due to the chemical chanoes in the respired air which are effected in the lungs. These movements may be, to a certain extent, controlled by the will; but every one is conscious, from his own sensations, that after a time the physical stimulus is capable of conquering the restraining influence of the mind; a striking example of a mental stimu lus giving way to a physical one, and illustra tive of the doctrine that the same fibres are affected by both stimuli. The exeitation of the medulla oblongata in respiration does not, however, depend solely upon the pul monary nerves. Those of the skin are ca pable of exciting it, either directly as the fifth pair, or through the spinal cord, as is proved by the inspirations which are instantly excited by suddenly dashing cold water on the face or trunk.