x] of the Nervous System. 277 



In the above Willis may be regarded as dimly striving to 

 explain nervous phenomena on the hypothesis of a specific 

 nervous fluid, possessed of peculiar properties, a kind of fore- 

 shadowing of an electric fluid. But when he comes to explain 

 the functions of the several cerebral structures he falls back on 

 his hypothesis of nervous action being light, or rather he falls 

 back on his illustration of light. Though the basis of the 

 sensitive soul, namely the animal spirits diffused through the 

 whole nervous system, is a physical, elastic fluid, the impres- 

 sions on it which are developed into sensations are no longer 

 regarded as impulses, as in the passage which I quoted just 

 now, but as optic images. 



The impressions made upon the sensory nerves by all 

 external objects pass through the middle parts of the brain, 

 through the crura cerebri to the corpora striata, thence to the 

 corpus callosum and so to the cortex. This is what he says : 



" As regards the various functions and duties of the spirits 

 " thus arranged in separate provinces, in the first place we allot 

 "to them a twofold feature, one by which they work inwards 

 " to carry on sensation, another by which they work outwards 

 " to carry on movement. More particularly it seems allowable 

 " to conceive of the middle regions of the brain as constituting 

 "an inner chamber of this soul fitted with dioptric mirrors, 

 "as with windows. The pictures or images of all sensible 

 " things admitted into these secret places by means of the 

 "ducts of the nerves, as by means of tubes or narrow openings, 

 " first pass through the corpora striata, which serves the purpose 

 "of an objective glass, and then are represented on the corpus 

 " callosum as on a whitened wall. And so the things which 

 " give rise to sensation induce perception and a certain imagi- 

 " nation. These images or pictures thus formed there very 

 " often produce nothing but the mere knowledge or sensation 

 "of the object, but presently or at times having passed on, as 

 " it were by a second undulation from the corpus callosum 

 " towards the cortex of the brain, and being stored in its folds, 

 " give rise to the memory of the thing, though the mere image 

 " vanishes. But if the particular sensation impressed on the 

 "imagination gives promise of something good or evil, forth- 



