OPTIC THALAMI. 721 



Their rounded base is directed forward, and the narrower end, backward and outward. 

 Their external surface is gray, and they present, on section, alternate striae of white and 

 gray matter, which appearance has given them the name of corpora striata. Between 

 the narrow extremities of these bodies, are situated the optic thalami. 



There is very little to be said with regard to the functions of the corpora striata. 

 Burdon- Sanderson has lately shown that, when the corpus striatum on one side, exposed 

 by carefully removing a small portion of the anterior lobe of the cerebrum, is stimulated 

 with a weak induced current of galvanism, movements of the muscles occur upon the oppo- 

 site side of the body. If the deepest parts be stimulated, " the animal opens its mouth, 

 puts out its tongue, and draws it in again alternately." "When the corpora striata are 

 removed, disturbing the hemispheres as little as possible, there appears to be no paralysis, 

 either of motion or sensation. 



We have obtained a little more information regarding the functions of the corpora 

 striata, from cases of cerebral haemorrhage in the human subject, than from experimental 

 investigations. In apoplexy, when the corpus striatum on one side is alone involved, 

 there is paralysis of motion of the opposite lateral half of the body, the general sensibility 

 usually being unaffected. Facts of this kind show that the action of the corpora striata 

 is crossed ; and they farther illustrate their connection with the motor tract from the 

 hemispheres. 



There is no reason to suppose that the corpora striata are the centres of olfaction, as 

 Avas at one time thought, for they are sometimes absent in animals possessing very large 

 olfactory nerves, and they are very largely developed in the cetacea, in which the olfac- 

 tory apparatus is rudimentary. 



Optic Thalami. 



From their name, we should infer that the optic thalami have some important func- 

 tion in connection with vision ; but they serve merely as beds for the optic commissures 

 and give to the nerves but very few fibres. They are oblong bodies, situated between 

 the posterior extremities of the corpora striata, and resting upon the crura cerebri on the 

 two sides. They are white externally, and, in their interior, present a mixture of white 

 and gray matter. Longet has destroyed them upon the two sides, carefully avoiding 

 injury of the optic tracts, and he noted no interference with vision or with the move- 

 ments of the iris. 



The optic thalami seem, from experiments upon animals, to have a peculiar crossed 

 action upon the muscular system. While their mechanical irritation produces neither 

 pain nor convulsive movements, showing that they are probably insensible and inexcita- 

 ble, the extirpation of one optic thalamus is followed by enfeeblement of the muscles of 

 the opposite lateral half of the body, without actual paralysis. When both have been 

 removed, there is general debility of the muscular system. It is unnecessary to refer to 

 other experiments upon these parts, which have been very indefinite in their results, or to 

 allude to the " circular " movements produced by lesion upon one side, involving also 

 the crus cerebri ; for, beyond the statement just made, the function of the optic thalami 

 is unknown. 



We derive but little information concerning the optic thalami from cases of cerebral 

 haemorrhage in the human subject ; for it is not common to have disease involving these 

 parts and not affecting other centres. In some cases of lesion limited to the optic thala- 

 mus on one side, there is paralysis of sensation of the opposite lateral half of the body, 

 without actual paralysis of motion, although the movements are generally feeble. When 

 the brain-lesion involves both the corpus striatum and the optic thalamus on one side, 

 which is more common, there is paralysis of motion, with loss or disorder of sensibility, 

 on the opposite side of the body. These facts illustrate, to a certain extent, the anatomi- 

 cal connection of the optic thalami with the sensory tracts, although, in experiments upon 

 animals, destruction of these parts does not necessarily affect the general sensibility. 

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