658 FUNCTIONS OF THE CEREBRO -SPINAL NERVOUS SYSTEM. 



Quadrigemina has been observed, both by Flourens and Longet, to produce 

 contraction of the pupils of both eyes. Budge has corroborated Flourens's 

 statements, adding that it is only when the lesion affects the inner part of 

 the corpora quadrigemiua, that paralysis of the Iris occurs, and that this 

 paralysis is on the side opposite to the lesion. Renzi admits there is tem- 

 porary, but denies there is permanent loss of contractility of the Iris. Knoll l 

 found that irritation of the anterior pair of the corpora quadrigemina caused 

 dilatation of both pupils, but especially of that of the same side. Lesions of 

 the corpora quadrigemiua were without effect on the iris, as long as the optic 

 tracts were untouched, but when these were damaged between the corpora 

 quadrigemina and the chiasma, paralysis of the opposite iris occurred, while 

 lesions of the optic nerve on the distal side of the chiasma caused paralysis 

 of the iris of the same side, showing that the fibres of the optic nerve which 

 excite refiectorially the iridal branches of the third nerve, undergo complete 

 decussation in the chiasma. Knoll operating on Rabbits, did not observe 

 any alteration in their motility after injuries inflicted upon the corpora 

 quadrigemina. These results of experiments are partly confirmed by Path- 

 ological phenomena in Man ; for there are many instances on record, in 

 which blindness has been one of the consequences of diseased alterations in 

 one or both tubercles; and in some of the cases in which the lesion extended 

 to parts seated beneath the tubercles, disturbed movements were observed. 

 The subservience of these bodies to the exercise of the visual sense, appears, 

 on the whole, to be the point best established in regard to their functions; 

 and considering the degree in which this sense is concerned in the regula- 

 tion of the general movements of the body, it is not surprising that lesions 

 of its centre should occasion a perversion of these movements. This appears 

 the more probable from the fact that, in animals whose Sensory ganglia 

 bear so large a proportion to the whole Encephalou that we must look upon 

 them as the principal centres of motor activity, instead of being chiefly con- 

 cerned (as in Man) in the mere guidance of movements whose origin is 

 Cerebral, lesions of the organ of sense from which the impressions that ex- 

 cite the seusori-motor impulses are derived, produce a corresponding dis- 

 turbance. Thus Flourens found that a vertiginous movement may be in- 

 duced in Pigeons by simply blinding one eye; aud Louget produced the 

 same effect by evacuating the humors of the eye. 



526. It is probably on the same principle, that we are to account for the 

 remarkable results obtained by Flourens 2 from section of the portion of the 

 Auditory nerve proceeding to the Semicircular canals. Section of the hori- 

 zontal semicircular canal in Pigeons, on both sides, induces a rapid jerking 

 horizontal movement of the head, from side to side; and a tendency to turn 

 to one side which manifests itself whenever the animal attempts to walk for- 

 wards. Section of a vertical canal, whether the superior or interior, of both 

 sides, is followed by a violent vertical movement of the head. And section 

 of the horizontal and vertical canals, at the same time, causes horizontal 

 and vertical movements. Section of either canal on one side only, is 

 followed by the same effect as when the canal is divided on both sides; but 

 this is inferior in intensity. The movements continue to be performed 

 during several mouths, but cease immediately if the thalami optici be re- 

 moved (Lowenberg). In Rabbits, section of the horizontal canal is followed 

 by the same movements as are exhibited by Pigeons; and they are even 

 more constant though less violent. Section of the anterior vertical canal 



1 (Vntnill.hitt f. cl. Mod. Wiss., 1872, p. 205. 



2 Op. cit. Src- also Botteher, Cent ralhlalt f. d. Med. Wiss., 1873, p. 72; and Lowen- 

 berg, idem, p. 278; Waldoyer, idem, 1872, p. 385. 



