OPTIC THALAm. 395 



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 mixfure of white and gray matter. Longet has 

 destroyed them upon the two sides, carefully avoiding injury 

 of the optic tracts, and noted* no interference with vision or 

 the movements of the iris. 



The optic thalarni 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 arc insensible and 

 in excitable, the extirpation of one optic thalamus produces 

 enfeeblemeiit of the muscles of the opposite lateral half of 

 the body, without actual paralysis. 1 "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 thalamus on one side, there is 

 paralysis of sensation of the opposite lateral half of the body, 

 without actual paralysis of motion, though 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 ana- 



1 LGXGET, Traite de jthysioloffie, Paris, 1869, tome iii., pp. 412, 413. 



