628 Dynamic Theory. 



causes various motions, according to the part operated upon. When 

 the posterior pair ( testes ) were stimulated the result was noises of vari- 

 ous kinds. When the stimulation was applied to the anterior pair 

 (nates), the muscles of the back were violently contracted, causing a 

 backward somersault, the jaws were clenched, and the pupils dilated. 



These results call to mind those which follow stimulations of the cere- 

 bellum, and tend to confirm the conclusions reached ; viz., that muscu- 

 lar co-ordinations, and the maintenance of equilibrium, are involved in 

 the integrity of the organs of sight. It is true that if the optic gan- 

 glions are entirely destroyed, it is possible that equilibration ma} r be re- 

 covered through the functions of the muscular, tactile and auditory 

 senses, but those co-ordinations can of course no longer be effected 

 which depend upon sight stimuli for their data. It does not appear to 

 follow that the corpora quadrigemina are of themselves a complete or- 

 gan for the conversion of its sensory into motor stimulations, ( although 

 such appears to have been the opinion of some physiologists ). But 

 these tubercles in connection with the corpora striata and optic thalami, 

 or with corpora striata alone, do certainly form such a complete ma- 

 chine, the corpora striata being composed, as will be shown, of motor 

 ganglions exclusively, and depending entirely on the corpora quadri- 

 gemina and optic thalami for afferent stimulations to make over into 

 motor ones. 



The optic lobes are probably something more than the mere organs of 

 sight sensations. In them, the single and simple sight sensations are 

 consolidated and condensed before they are forwarded to the organs of 

 memory in the cerebrum. The eye is like a photographic instrument. 

 When it is focused upon an object, every detail of that object reflects 

 its light as a stimulus upon a cell of the optic lobes. If we look at a 

 brick house, or a tree, we must see all the bricks and all the leaves that 

 go to make up the general impression of a house and a tree, although 

 we cannot recall any particular brick or leaf. All of these details are 

 for a moment impressed upon the cells of the optic lobes, but are there 

 probably so far consolidated that when the stimulations are darted for- 

 ward toward the optic thalamus and the cerebrum, they are generalized 

 into the single stimuli of house and tree. The same is true, no matter 

 how small the object under consideration. Thus, if we look at a leaf, 

 we undoubtedly see all its details of veins and veinlets, serrations, 

 wrinkles, and various shades of coloring. But all these details may be- 

 come so far suppressed, or merged into the general image of the leaf, 

 that they cannot be recalled in the memory cells of the cerebrum, the 

 general image alone being registered there. Such condensations as 

 these, 1 take it, are accomplished in the corpora quadrigemina. 



Optic Thalamus. This name is inappropriate, because the organ so 



