PHYSIOLOGY OF THE NERVOUS SYSTEM. 



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traction of the pupils. Longet found that re- 

 moval of one optic thalamus in the rabbit was 

 followed by paralysis on the opposite side of 

 the body. It appears, however, that this was 

 done after the removal of the hemisphere and 

 corpus striatum, whereby the experiment was 

 so complicated as to invalidate any conclusion 

 that might be drawn from it respecting the 

 function of the thalamus. Indeed, vivisections 

 upon so complex an organ as the brain are ill- 

 calculated to lead to useful or satisfactory 

 results; but one does not hesitate to refer to 

 such as have been made, because they afford a 

 certain amount of negative information, imper- 

 fect though it be. 



Nothing definitive respecting the proper 

 office of the thalami can be obtained from pa- 

 thological anatomy. Extensive disease of 

 these bodies is attended with the same phe- 

 nomena during life, as lesion of similar kind 

 in the corpora striata. Ilemiplegic paralysis 

 accompanies both : nor does it appear that sen- 

 sation is more impaired when the thalamus is 

 diseased, than when the corpus striatum is 

 affected . 



There is nothing in the phenomena attendant 

 on morbid states of the thalami which can be 

 fairly regarded as opposed to the conclusion 

 which their anatomical relations indicate, name- 

 ly, that they form a principal part of the centre 

 of sensation. The intimate connection between 

 the striated bodies and the thalami sufficiently 

 explains the paralysis of motion which follows 

 disease of the latter; whilst, as the thalami do 

 not constitute the whole centre of sensation, but 

 only a part thereof, it cannot be expected that 

 lesion of this part would destroy sensation, so 

 long as the remainder of the centre on the same 

 side, as well as that of the opposite side, retain 

 their integrity. Complete paralysis of sensation 

 on one side is very rare in diseased brain : a 

 slight impairment of it frequently exists in the 

 early periods of cerebral lesion, apparently as 

 an eflect of shock ; for it quickly subsides, 

 although the motor power may never return. 



According to the views above expressed, the 

 corpora striata and optic thalami bear to each 

 other a relation analogous to that of the ante- 

 rior to the posterior horn of the spinal grey 

 matter. The corpora striata and anterior horns 

 are centres of motion ; the optic thalami and 

 posterior horns, centres of sensation. The 

 anterior pyramids connect the former; the 

 olivary columns, and perhaps some fibres of 

 the anterior pyramids, the latter. The olivary 

 columns, however, are in great part continu- 

 ations of the thalami on the one hand, and of 

 the grey matter of the cord on the other ; and 

 contain abundance of vesicular matter, in which 

 nerves are implanted. 



And it must be admitted that the intimate 

 connection of sensation and motion, whereby 

 sensation becomes a frequent excitor of mo- 

 tion, and voluntary motion is always, in a 

 state of health, attended with sensation, 

 would priori lead us to look for the respec- 

 tive centres of these two great faculties, not 

 only in juxta-position, but in union at least as 

 intimate as that which exists between the corpus 



striatum and optic thalamus, or between the 

 anterior and the posterior horns of the spinal 

 grey matter. 



Saucerotte, Foville, Pinel Grandchamps, and 

 others, advanced the opinion that the corpora 

 striata and the fibrous substance of the anterior 

 lobes of the brain had a special influence upon 

 the motions of the lower extremities, and that 

 the optic thalami and the fibrous substance of 

 the middle and posterior part of the brain pre- 

 sided over the movements of the upper ex- 

 tremities. We find, however, but little to 

 favour this theory either in the results of ex- 

 periments, in pathological observation, or the 

 anatomy of the parts. Longet states, that, in 

 his experiments upon the optic thalami, the 

 paralysis affected equally the anterior and the 

 posterior extremities. Andral analysed se 

 venty-five cases of cerebral lesion limited to 

 the corpus striatum or optic thalamus. In 

 twenty-three of these cases, the paralysis was 

 confined to the upper extremity: of these, 

 eleven were affected with lesion of the corpus 

 striatum or of the anterior lobe; ten with lesion 

 of the posterior lobe, or of the optic thalamus; 

 and two with lesion of the middle lobe.* 

 Hence it is plain that a diseased state of the 

 corpus striatum is as apt to induce paralysis 

 of the upper extremity as lesion of the tha- 

 lamus ; and we are forced to conclude, that 

 pathological anatomy is not competent to de- 

 cide the question. Lastly, the anatomy of these 

 two bodies renders it highly improbable thai 

 they perform a function so similar, as that of 

 directing the movements of particular limbs. 

 The great size of the optic thalamus, its mul- 

 titude of fibrous radiations, its extensive con- 

 nections both in the medulla oblorigata and in 

 the hemispheres by means of commissural 

 fibres, the marked difference of its structure 

 from that of the corpus striatum, its con- 

 nection more with the posterior horns of the 

 spinal grey matter than with the anterior ones, 

 and its intimate relation to nerves of sensation, 

 are sufficient anatomical facts to warrant the 

 opinion that the thalami must perform a func- 

 tion which, although it may be subservient to, 

 or associated with, that of the striated bodies, 

 is yet entirely dissimilar in kind. 



It has been supposed that the corpora striata 

 are special centres or ganglia to the olfactory 

 nerves, and to the sense of smell. But such 

 a supposition is altogether superfluous, inas- 

 much as a very distinct and obvious centre to 

 these nerves exists in the olfactory process or 

 lobe, miscalled nerve by descriptive anatomists. 

 The small olfactory nerves are implanted in 

 the anterior extremity or bulb of this process, 

 which is provided with all the structural cha- 

 racters of a nervous centre, and contains a 

 ventricle. This lobe, moreover, is always de- 

 veloped in the diiect ratio of the size and 

 number of the olfactory nerves, and of the 

 developement of the sense of smell; and in 

 the Cetacea, a class in which the olfactory 

 nerves and process either do not exist at all, 

 or are so imperfectly developed as to have 



* Clin. Mod. t. v. 



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