358 Proceedings of the Royal Society 
ganglion on the opposite side of the head, while the fibres on the 
outer side of each eye went to the ganglion on their own side of 
the head. This explanation evidently implies that the retinse are 
optically divided in two halves, and that the images of objects 
falling on the centres of the retinse are similarly divided, one half 
of every object being represented on the right side of the head, 
and the other half on the left ; and that objects whose images fall 
on the one side of the retinae are represented only on the lobe on 
that side of the head. This is surely extremely improbable. 
Newton, in his optics, throws out a query (query 15th at the 
end of Second Book), suggesting that the species or picture of the 
objects seen with both eyes may be united in the commissure of 
the optic nerves, the fibres of the right side of both nerves uniting 
there, and, after union, going tfience into the brain on the right 
side of the head, and the fibres on the left side of both nerves, after 
union in the commissure, going into the brain on the left side of 
the head, and the two meeting in the brain in such a way that the 
fibres make but one entire species or picture. The writer had not 
seen Newton’s query till after his paper was submitted to the 
Council, but he considers that Newton’s is the most advanced 
position which has up to the present times been taken on the 
subject. It is evident, however, that Newton had never very 
carefully reduced his idea to form, nor had he then the means 
which we now possess of testing its correctness; and it was 
doubtless owing to this circumstance that the idea, instead of being 
followed up and corrected in its details, was allowed to fall out of 
sight, and failed to gain the attention of optical writers. 
Whether there is or is not a crossing of the true visual or optic 
nerves in man and the higher mammalia seems yet to be an 
unsettled point, though the opinion is gaining ground that there 
is a crossing of the inner fibres. It is always asked if there is no 
crossing of fibres, why are the optic nerves brought into connection ? 
The question, as an argument in favour of the crossing, is, how- 
ever, robbed of half its force, when we consider that the apparent 
union of the commissure may not be for a transfer of the true 
nerves of vision, but for effecting a union of the nerves essential 
for the nutrition of the retinse, and of those nerves whose func- 
tion it is to secure equality and unity of action in the reflex opera- 
