PHYSIOLOGY OF THE NERVOUS SYSTEM. 



722L 



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 exciting cause is probably, 

 as Dr. Hall suggested, due to the chemical 

 changes 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 excitation 

 of the medulla oblongata in respiration does 

 not, however, depend solely upon the pul- 

 monary nerves. Those of the skin a<-e 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. 



In deglutition, the exciting cause is the sti- 

 mulus of contact applied to the mucous mem- 

 brane of the fauces. So highly sensitive is the 

 mucous membrane in this situation, that the 

 slightest touch of it with a feather is sufficient 

 to produce contraction of the muscles of deglu- 

 tition, which the will is scarcely able to con- 

 trol. Without this stimulus, it is doubtful 

 whether these muscles would obey the will 

 alone, and it seems probable that this part of 

 the act of deglutition must be regarded as one 

 of those actions referred to at a former page, 

 which requite a double stimulus, both mental 

 and physical, for their full performance. 



The medulla oblongata and its continuations 

 in the mesocephale appear to be the centre of 

 those actions which are influenced by emotion. 

 The common excitement of movements of de- 

 glutition or respiration, or of sensations referred 

 to the throat, under the influence of emotion, 

 evidently points to this part of the cerebro- 

 spinal centre as being very prone to obey such 

 impulses; and as the nerves of pure sense, 

 especially the optic and auditory, are very 

 commonly the channels of sensitive impressions 

 well calculated to arouse the feelings, it seems 

 highly probable that the centre of such actions 

 should be contiguous to the origin of these 

 nerves. This office may be assigned to that 

 region of the mesocephale which is in the 

 vicinity of the quadrigeminal tubercles. It is 

 not a little remarkable that the nerves which 

 arise from this and the neighbouring parts are 

 very readily influenced by emotions. Thus, 

 the third and fourth pairs of nerves regulate 

 the principal movements of the eyeballs, those 

 especially which most quickly betray emotional 

 excitement; and the portio dura of the se- 

 venth pair, the motor nerve of the face, is the 

 medium through which changes of the counte- 

 nance are effected. It may be added, that the 

 centre of emotional actions ought to be so situ- 

 ated that it might readily communicate with 

 the centres of all the voluntary actions of the 

 body, and with the immediate seat of the 

 intellectual operations, as well as with the 



VOL. III. 



nerves of pure sense; and no part possesses 

 these relations so completely as that now under 

 examination. 



In those diseases which mental emotion is 

 apt to give rise to, many of the symptoms are 

 referable to affection of the medulla oblongata. 

 In hysteria, the globus, or peculiar sense of 

 suffocation or constriction about the fauces; in 

 chorea, the difficulty of deglutition, the pecu- 

 liar movement of the tongue, the excited state 

 of the countenance, the difficulty of articula- 

 tion, may be attributed to the exalted polarity 

 of the centre of emotional actions. In hydro- 

 phobia this part is probably always affected, 

 and frequently so in tetanus. 



Certain gangliform bodies are connected with 

 the upward continuations of the medulla ob- 

 longata, both in the brain and in the mesoce- 

 phale, which doubtless have proper functions. 

 These are the corpora striata, optic thalami, 

 and quadrigeminal bodies. 



Corpora striata. The anatomy of the cor- 

 pora striata and optic thalami, while it denotes 

 a very intimate union between them, also shows 

 so manifest a difference in their structural cha- 

 raclers, that it cannot be doubted that they 

 perform essentially different functions. In the 

 corpora striata the fibrous matter is arranged 

 in distinct fascicles of various sizes, many, 

 if not all of which, form a special connection 

 with its vesicular matter. In the optic thala- 

 mi, on the other hand, the fibrous matter forms 

 a very intricate interlacement, which is equally 

 complicated at every part. Innumerable fibres 

 pass from one to the other, and both are con- 

 nected to the hemispheres by extensive radia- 

 tions of fibrous matter. The corpora striata, 

 however, are connected chiefly, if not solely, 

 with the inferior fibrous layer of each crus 

 cerebri; whilst the optic thalami are continuous 

 with the superior part of each crus, which is 

 situate above the locus niger. 



It will be observed, then, that while these 

 bodies possess, as a principal character in com- 

 mon, an extensive connection with the convo- 

 luted surface of the brain, they are, in the most 

 marked way, connected inferiorly with separate 

 and distinct portions of the medulla oblongata; 

 the corpora striata with the inferior fibrous 

 planes of the crura cerebri and their continua- 

 tions, the anterior pyramids ; and the optic 

 thalami with the olivary columns, the central 

 and probably fundamental portions of the me- 

 dulla oblongata. This anatomical fact must 

 be taken as an additional indication that these 

 gangliform bodies perform separate functions. 



Now, it may be inferred, from their con- 

 nections with nerves chiefly of a sensitive kind, 

 that the olivary columns, and the optic thalami, 

 which are continuous with them, are chiefly 

 concerned in the reception of sensitive impres- 

 sions, which may principally have reference 

 merely to informing the mind (so to speak), or 

 partly to the excitation of motion, as in deglu- 

 tition, respiration, &c. The posterior horns of 

 the grey matter of the cord, either by their 

 direct continuity with the olivary columns, or 

 their union with these columns through com- 



missural fibres, become part and parcel of a 



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