638 CORPORA QUADRIGEMINA. [BOOK m. 



confined to an optic thalamus has caused loss of movement as well 

 as of sensation. 



The evidence obtained by means of experiments on animals is 

 still more discordant. Some observers have found that stimulation, 

 either mechanical or electrical, of the corpora striata gives rise to 

 convulsive movements, while stimulation of the optic thalami does 

 not ; and have seen in these results a confirmation of the view we 

 are discussing. Such a confirmation is, at best, a feeble one, and 

 moreover is not supported by the results of all observers. Some 

 observers again have found that removal or destruction, by the 

 injection of corrosive substances, of both nuclei lenticular es (the 

 extra-ventricular portions of the corpora striata) leads to a sup- 

 pression of voluntary movements almost as complete as if both 

 hemispheres were removed, whereas after removal or destruction of 

 both nuclei caudati (intra-ventricular portions of the same bodies) 

 voluntary movements still persist ; and it has been affirmed that 

 the removal or destruction of the optic thalami may with care be 

 effected without the animal appearing any the worse. In the 

 absence of more exact knowledge it is useless to attempt to form 

 any clear judgment ; and the view we stated above as to the motor 

 functions of the corpora striata and sensory functions of the optic 

 thalami may be allowed to stand as neither definitely disproved 

 nor satisfactorily proved, and as in any case affording an inadequate 

 expression of the part played by these masses in the general work 

 of the brain. Two points we may venture to call attention to, 

 which as far as they go may be used as arguments in support of 

 the above view. Almost all observers agree that after injuries 

 to the corpora striata, more particularly after one-sided or after 

 partial injuries, and especially after injuries of the nuclei caudati, 

 forced movements such as those of which we spoke on p. 620 are 

 very apt to make their appearance. With regard to the optic 

 thalami on the other hand there is an agreement both of experi- 

 mental and pathological evidence in favour of the view (which as 

 the very name of the bodies shews is an old one) that these 

 structures are in some way or other concerned in vision. Where 

 the optic thalami are directly involved in an injury to or disease of 

 the brain, blindness or at least some imperfection of vision is a 

 frequent result ; and there are reasons for thinking that in some at 

 all events of the cases where blindness has resulted from removal 

 of the cerebral cortex of the hinder part of the hemispheres, the 

 optic thalami have been either directly or secondarily affected. 



Corpora Quadrigemina. We have already seen that the centre 

 of coordination for the movements of the eyeballs (p. 546), and that 

 for the contraction of the pupil (p. 501), lie in the neighbourhood of 

 the upper or anterior pair of the corpora quadrigemina. These 

 two centres are associated together in such a way that when the 

 eyeballs are voluntarily directed inwards and downwards, as for near 



