224 Dr. Wollaston on semi-decussation 
the left eye, while the right eye is supplied entirely from 
fibres arising from the left thalamus. 
In this opinion, anatomists have felt themselves confirmed 
by the result of their examination of other animals, and 
especially that of several species of fish, in which it is dis- 
tinctly seen that the nerves do actually cross each other as a 
pair of separate cords, lying in contact at their crossing, but 
without any intermixture of their fibres. 
In these cases it is most indisputably true, that the eye upon 
the right side of the animal does receive its optic nerve from 
the left side of the brain, while that of the left eye comes from 
the right side ; but it is not a just inference to suppose the 
same continuity preserved in other animals, where such com- 
plete separation of the entire nerves is not found. 
On the contrary, I not only see reason, from a species of 
blindness which has happened to myself more than once, to 
conclude, that a different distribution of nerves takes place in 
us, but I think my opinion supported by this evident difference 
of structure in fishes. 
It is now more than twenty years since I was first affected 
with the peculiar state of vision, to which I allude, in conse- 
quence of violent exercise I had taken for two or three hours 
before. I suddenly found that I could see but half the face 
of a man whom I met ; and it was the same with respect to 
every object I looked at. In attempting to read the name 
Johnson, over a door, I saw only son ; the commence- 
ment of the name being wholly obliterated to my view. In 
this instance the loss of sight was toward my left, and was 
the same whether I looked with the right eye or the left. This 
