CORPORA STRIATA. HEMISPHERES. 419 



the optic thalami have been thoroughly disorganized ; and that arti- 

 ficial irritation of the same ganglia has no effect in producing 

 either contraction or dilatation of the pupil. The optic thalami, 

 however, according to the same observer, have a peculiar crossed 

 action upon the voluntary movements. If both hemispheres and 

 both optic thalami be removed in the rabbit, the animal is still 

 capable of standing and of using his limbs in progression. But if 

 the right optic thalamus alone be removed, the animal falls at once 

 upon his left side ; and if the left thalamus be destroyed, a similar 

 debility is manifest on the right side of the body. In these in- 

 stances there is no absolute paralysis of the side upon which the 

 animal falls, but rather a simple want of balance between the two 

 opposite sides. The exact mechanism of this peculiar functional 

 disturbance is not well understood ; and but little light has yet 

 been thrown, either by direct experiment or by the facts of compa- 

 rative anatomy, on the real function of the optic thalami. 



CORPORA STRIATA, The function of these ganglia is equally 

 uncertain with that of the preceding. They are traversed, as we 

 have already seen, by fibres coming from the anterior columns of 

 the cord; and they are connected, by the continuation of these 

 fibres, with the gray substance of the hemispheres. They have 

 therefore, in all probability, like the optic thalami, some connection 

 with sensation and volition ; but the precise nature of this connec- 

 tion is at present altogether unknown. 



HEMISPHERES. The hemispheres, or the cerebral ganglia, con- 

 stitute in the human subject about nine-tenths of the whole mass 

 of the brain. Throughout their whole extent they are entirely 

 destitute, as we have already mentioned, of both sensibility and ex- 

 citability. Both the white and gray substance may be wounded, 

 burned, lacerated, crushed, or galvanized in the living animal, with- 

 out exciting any convulsive movement or any apparent sensation. 

 In the human subject a similar insensibility has been observed 

 when the substance of the hemispheres has been exposed by acci- 

 dental violence, or in the operation of trephining. 



Yery severe mechanical injuries may also be inflicted upon the 

 hemispheres, even in the human subject, without producing any 

 directly fatal result. One of the most remarkable instances of this 

 fact is a case reported by Prof. William Detmold, of New York, 1 in 



1 Am. Journ. of Med. Sci., January, 1850. 



