GANGLION OF <THE TUBEE ANNCLAEE. 399 



The above experiments, it is true, are not as free iroin 

 uncertainty as those made upon the more accessible parts of 

 the eneephalon, but, as far as they go, they tend to show 

 that the tuber annulare is both insensible and inexcitable in 

 its superficial anterior portion, which is composed chiefly of 

 commissural fibres from the cerebellum ; that it is excitable 

 and probably insensible in its deeper anterior portion, which 

 seems to be composed chiefly of descending motor conduct- 

 ors ; and finally, that it is sensible and probably inexcitable 

 in its posterior portion. 



The tuber annulare undoubtedly acts as a conductor of 

 sensory impressions and motor stimulus to and from the 

 cerebrum, as we would naturally expect from the direction 

 of its fibres, and as has been repeatedly shown by cases of 

 disease, particularly as regards motion. In addition, how- 

 ever, judging from the fact that it contains numerous nod- 

 ules of gray matter between fasciculi of white fibres, and 

 that this gray matter contains cellular elements similar to 

 those found in other nerve-centres, and from which new 

 nerve-fibres undoubtedly originate, it would be inferred 

 that these nodules have a distinct function, and give to the 

 tuber annulare the properties of a nerve-centre. It will be 

 interesting, therefore, to follow out the experiments upon 

 this part, by which its action as a centre has been illustrated. 

 These experiments are of two kinds : First, the removal of 

 other encephalic ganglia, leaving only the tuber annulare, 

 the medulla oblongata, and the cerebellum, and noting the 

 properties or faculties retained by animals under these con- 

 ditions. Experiments of this kind are tolerably definite, as 

 we already know the general functions of most of the other 

 encephalic ganglia. Second, to note the effects of extirpa- 

 tioTi of the tuber annulare alone. 



If the cerebral hemispheres, the olfactory ganglia, the 

 optic lobes, the corpora striata, and the optic thalami, be 

 removed, the animal loses the special senses of smell and 

 sight and the intellectual faculties, there is a certain amount 



128 



