CHAP. XI.] FUNCTIONS OF THE OPTJC THALAMI. 349 



Majendie. Removal of the corpus striatum of one side caused 

 weakness of the opposite side. 



In order to form a due estimate of these experiments, it must be 

 borne in mind, that the effects of simple excision of either corpus 

 striatum would be very different from those of disease of it. The 

 depressing effects of the latter would be absent, at least, until some 

 alteration in the process of nutrition had been set up in the mutilated 

 parts. Simple excision of the centre of volition, and inflammatory 

 disease of its substance, or an apopletic clot, must produce essen- 

 tially different effects ; the one simply cuts off the influence of 

 the will, the other affects the vital action, and, consequently, the 

 vital power of the centre, and of the commissural fibres connected 

 with it. 



Judging from structure only, it might be conjectured that the 

 locus niger, that remarkable mass of vesicular matter which sepa- 

 rates the anterior and posterior planes of each crus cerebri, exerts a 

 motor influence. It resembles in structure the anterior horns of 

 the gray matter of the cord, and contains numerous large caudate 

 vesicles with very abundant pigment. 



Optic Thalami. The same line of argument which leads us to 

 view the corpora striata as the more essential parts of the nervous 

 apparatus which control direct voluntary movements, suggests that 

 the optic thalami may be viewed as the principal foci of sensibility, 

 without which the mind could not perceive the physical change 

 resulting from a sensitive impression. 



The principal anatomical fact which favours this conclusion, is 

 the connexion of all the nerves of pure sense, more or less directly, 

 with the optic thalami or with the olivary columns. The olfactory 

 processes, which apparently have no connexion with them, form, no 

 doubt, through the fornix, such an union with them, as readily 

 to bring them within the influence of the olfactory nerves. 



According to this sense of its office, we must regard the optic 

 thalami as the upper and chief portions of an extended centre, of 

 which the lower part is formed by the olivary columns, whicK we have 

 already referred to as taking part in the mechanism of sensation. 

 The continuity of the olivary columns with the optic thalami jus- 

 tifies this view : nor is it invalidated by the fact, that some of the 

 nerves wli'idi arise from the medulla oblongata are motor in 

 function ; for Stilling's researches render it probable that these 

 fibres have their origin in special accumulations of vesicular matter, 

 which contain caudate vesicles of the same kind as those found in 

 the anterior horns of the gray matter of the cord. (See fig 70). 



