722o 



PHYSIOLOGY OF THE NERVOUS SYSTEM. 



escaped the notice of some of the ablest ana- 

 tomists, the corpora striata are of good size 

 proportionally to that of the entire brain. 



Corpora quadrigeminu. The marked con- 

 nection of these gangliforrn bodies with the 

 optic nerves plainly indicates that they bear 

 some special relation to those nerves, and to 

 the sense of vision ; and this indication be- 

 comes more certain when we learn, from com- 

 parative anatomy, that in all vertebrate tribes 

 in which the encephalon is developed, special 

 lobes exist, bearing a similar relation to the 

 optic nerves. When the optic nerves are large, 

 these lobes are large ; and in the Pleuronecta, 

 in which the eyes are of unequal size, Gottsche 

 states that the optic lobes are unequal, and are 

 related in size to each other, as the eyeballs are. 

 Still, as Sevres has remarked, the quadrigeminal 

 tubercles probably perform some other office 

 besides that which refers to vision ; inasmuch 

 as the absence, or extremely diminutive size, 

 of the optic nerves in some animals (the mole 

 for instance) does not materially affect that of 

 these bodies.* 



Flourens found that destruction of either of 

 these tubercles on one side was followed by 

 loss of sight of the opposite side, and con- 

 sequently that the removal of both deprived 

 the animal altogether of the power of vision, 

 but did not affect its locomotive or intellectual 

 powers, nor its sensibility, except to light. In 

 these experiments the action of the iris was 

 not impaired if the tubercles were only par- 

 tially removed ; as long as any portion of the 

 roots of the optic nerves remained uninjured, 

 the iris continued to respond to the stimulus 

 of light, but the total removal of the tubercles 

 paralysed the irides. If the lobes of the brain 

 and cerebellum were removed, leaving the 

 tubercles untouched, the irides would continue 

 to contract. These experiments leave no room 

 to doubt that the optic tubercles are the ence- 

 phalic recipients of the impressions necessary 

 to vision, which doubtless are simultaneously 

 felt by means of the optic thalami ; and that 

 they are the centres of those movements of the 

 iris which contribute largely not only to pro- 

 tect the retina, but likewise to increase the 

 perfection of vision. The optic nerve is at 

 once the nerve of vision, and the excitor of 

 motor impulses which are conveyed to the iris 

 by the third nerve, which takes its origin very 

 near to the optic tubercles. It is interesting 

 to add, that irritation of an optic tubercle on 

 one side causes contraction of both irides : 

 this is quite in accordance with the well- 

 established fact, that, if light be admitted to 

 one eye so as to cause contraction of its pupil, 

 the other pupil will contract at the same time. 

 So simultaneous is the action of the two cen- 

 tres ; so rapid must be the transmission of the 

 stimulus from one side to the other. 



When the injuries inflicted on these tuber- 

 cles were deep, more or less general convulsive 

 movements were produced ; if one tubercle 

 were injured, the opposite side only was so 

 affected. These convulsions were due to the 



* Vid. OPTIC NERVES.; 



lesion of the central parts of the medulla ob- 

 longata, with which the optic tubercles are in- 

 timately connected. A remarkable vertiginous 

 movement was likewise caused, the animal 

 turning to the side from which the tubercle had 

 been removed. It does not appear that this 

 rotation could be attributed to any special in- 

 fluence of the medulla oblongata, but rather to 

 a state of vertigo induced by the partial destruc- 

 tion of vision ; for Flourens found that the 

 same effects could be produced in pigeons by 

 blindfolding one eye. The movements, how- 

 ever, were not so rapid, nor did they continue 

 so long. And Longet saw the same movements 

 in pigeons in which he had evacuated the hu- 

 mours of one eye.* 



It may be remarked, that deep injuries to 

 the quadrigeminal tubercles are very likely to 

 affect the only commissural connection between 

 the cerebrum and cerebellum (processus ce.re- 

 belli ad testes), the integrity of which must 

 doubtless be essentially necessary to ensure 

 harmony of action between these two great 

 nervous centres. 



There are many instances on record in which 

 blindness was coincident with pathological 

 alteration of structure in one or both quadrige- 

 minal tubercles. In some of the cases where 

 the lesion extended to parts seated beneath the 

 tubercles, disturbed movements were observed, 

 as in the experiments above related. 



We are ignorant of the object of the exten- 

 sive connections of the optic tracts with the 

 tuber cinereum, the crura cerebri, and the cor- 

 pora geniculata; but these points are highly 

 worthy of future inquiry, especially with re- 

 ference to the office of these last-named bodies, 

 which is at present involved in much obscurity. 

 Many of the fibres of the optic tracts are un- 

 doubtedly commissural between the corres- 

 ponding points of opposite sides, and exist 

 when those which form the optic nerves are 

 deficient. 



We see, then, in the quadrigeminal tubercles, 

 centres, which, whatever other functions they 

 may perform, have a sufficiently obvious rela- 

 tion to the optic nerves, the eye, and the sense 

 of vision. This is clearly indicated by ana- 

 tomical facts, especially by those of compara- 

 tive anatomy, by the results of experiment, and 

 by the phenomena of disease. These bodies 

 may, therefore, be justly reckoned as special 

 ganglia of vision ; and we are led to seek for 

 similar centres in connection with the other 

 senses. The olfactory processes seem very 

 probably to perform a similar office in reference 

 to the sense of smell. Their structure, their 

 relation to the olfactory nerves, and their direct 

 proportion of bulk to that of these nerves, and 

 to the developement of the olfactory apparatus, 

 place this question beyond all doubt. It is not 

 so easy to determine the special ganglia of hear- 

 ing ; but the olivary bodies, or the small lo- 

 bules connected with the crura cerebelli called 

 by lleil the flocks, may be referred to as bearing 

 a sufficient close anatomical relation to the 



* Flourens' experiments have been amply con- 

 firmed by those of Hevtwig and Longet. 



