FUNCTIONS OF THE OPTIC THALAMI. 285 



The office of the corpora geniculata is unknown ; from their ana- 

 tomical connections, they might be supposed to be associated with the 

 exercise of the function of sight, but they may be merely sympathetic 

 ganglia. 



The large optic ihalami are supposed also to be concerned, in some 

 way, in the sense of vision, but not to the degree indicated by their 

 name ; for when they are completely destroyed or removed, the sense 

 of sight and the action of the pupil still remain. Irritation of the 

 optic thalami of one or both sides, is not followed by contraction of 

 the iris ; such irritation causes either no signs, or very slight indica- 

 tions, of pain, and no convulsions. Section of one, is followed by 

 rotatory movements, usually towards the opposite side, but, it is said, 

 in the frog, towards the injured side; such movements differ from similar 

 movements induced by injuries of other parts of the brain, in the fact 

 that the animal continues standing. After removal of the cerebral 

 hemispheres, including the corpora striata, the ability to stand and 

 walk remains ; but if one optic thalamus be cut away, the animal 

 either exhibits rotatory movements, or is paralyzed on the opposite 

 side and falls. (Longet.) It is stated by Schiflf, that when the anterior 

 three-fourths of the thalamus are destroyed, the rotation is towards 

 the injured side ; whereas, when the posterior fourth is destroyed, it 

 is towards the sound side. By some authorities, the optic thalami, 

 though themselves insensible to direct irritation, are believed to be 

 the great foci of all the sensory nerves, and their gray matter possi- 

 bly the common sensorium, or the nervous centre concerned in common 

 sensation. 



The functions of the corpora striata are also uncertain. Their re- 

 moval in rabbits, is said to leave sensation and voluntary motion 

 equally unimpaired ; for, though at first passive, after a time, on being 

 irritated, the animal manifests progressive movements of leaping, until 

 it meets with an obstacle, when it again becomes quiet. (Schiff.) Me- 

 chanical irritation of these bodies is said to produce neither pain nor 

 movement. Extravasation of blood into one corpus striatum, causes 

 paralysis of the muscles of the body on the opposite side, owing to the 

 decussation of the pyramids, and of the facial muscles usually on the 

 same side, though sometimes on the opposite side also ; why, is not 

 known. If convulsions occur, they are also usually on the same side 

 as the paralysis ; in this case, the corpora quadrigernina are also com- 

 monly injured. If paralysis happens on one side, and convulsions on 

 the other, there is usually lesion either of the corpus striatum, base 

 of the brain, or cerebral peduncles, and also of the medulla oblongata 

 on the same side, viz., on the side on which the convulsions occur. 



As the course of the posterior or afferent fibres of the peduncles, is 

 chiefly through the optic thalami, and the course of the anterior or 

 under set of efferent fibres, is chiefly through the corpora striata, it 

 has commonly been concluded that the corpora striata are chiefly con- 

 cerned in the function of motion, and the optic thalami in the function 

 of sensation ; but these views are more or less hypothetical. It has 

 also been suggested that both the corpora striata and the thalami are 

 sensory ganglia, and have the same relation to the nerves of touch, or 



