6l2 PHILOSOPHICAL TRANSACTIONS. [aNNO 1683. 



been propounded against It. In that small essay I endeavoured to show, 1. That 

 the fibres of the optic nerve, as rising from the two protuberances of the thalami 

 optici, were more concerned in vision then either the cornea, humours, or re- 

 tina ; not only because sensation is performed chiefly in the brain, and these 

 other parts are but the transennae to it; but also because in an amaurosis, or 

 gutta Serena, these parts are free from any indisposition, the eye appearing as 

 naturally without any fault, though the sight is then wholly lost. 2. I show 

 there that the superior fibre in each thalamus opticus had the greatest tension, 

 and the inferior the least; as may appear from the former arising from the top 

 of the thalami optici and having the greatest flexure thus o ; and the latter 

 arising from the lower part of the aforesaid thalami, and having the least flexure 

 thus ^. 3. It may be further noted, that the intermediate or lateral fibres in 

 the same eye, though diametrically opposite to each other, are said to differ in 

 tension, by reason of a more considerable flexure of the external then the inter- 

 nal. 4. 1 observed that the optic nerves arose separately from those two moleculae 

 of the brain, and besides have a peculiar advantage in rising from these hillocks 

 in this manner; whereas the other nerves arise from the basis of the brain in a 

 flatter manner, and closer together, so that the extreme difference of their rise 

 is very remarkable, and intended surely by nature for some extraordinary end. 

 5. In the position of the fibres of the optic nerves, I show that they keep their 

 distinct order, and consequently that they are not mixed or blended together 

 at the place of their connection, as was frivolously supposed by authors before 

 to solve the union of vision. 6. I observed that in the insertion of these fibres 

 into the eye, where the medullary part of them forms the retina, they still kept 

 their distinct series, and that they are much kept in, not only by being fastened 

 or terminating on the processus ciliares, but also by little transverse fibres, 

 which serve to connect those that run longwise, and make the whole coat ap- 

 pear in a glass of clear water like lawn or tiffany, as I have shown. None that 

 I know ever did it before me, and those that have mentioned the same experi- 

 ment since, have mistook my intent in it. For the putting the retina in water 

 is not to wash off the mucous substance, which is its proper substance; but to 

 expand the fibres by the playing it up and down in warm water, and to magnify 

 the image of it by a double refraction of the lucid rays, which pass through that 

 and the glass that contains it. 7. But next of all I would have it observed, that 

 whereas I say the intermediate fibres gradually diff'er in tension as they are nearer 

 or further from the top of the thalami optici, it may be easily supposed that they 

 do it by so minute gradations, that the difference of those that are higher to 

 the top from the superior of all is very little, but from those that are further 

 off great enough, and the difference of the highest fibres from the lowest. 



