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X. On Semi-decussation of the Optic Nerves. By William 
Hyde Wollaston, M. D. V. P. R. S. 
Read February 19, 1824. 
Whe ther we consider the astonishing subtlety of that 
medium, which renders visible to us objects existing at the 
most immeasurable distances from us, or that delicately con- 
stituted organ which, by its general structure, collects the 
rays of light, and by a nice adaptation of its parts concen- 
trates their force on the sentient fibres of the retina, expanded 
over its inner surface, we can feel no surprise that such great 
talents should have been devoted to investigate the curious 
properties of the one, or that the structure of the other should 
have been examined with so much assiduity. 
The keenness of inquiry manifested by the cultivators of 
anatomy in observing the most minute parts that have es- 
caped the notice of their predecessors, shows that any addi- 
tion to the common stock of our information on this subject 
will be gratifying to a certain portion of the members of this 
Society, and probably not uninteresting to the Society at 
large. 
It is not my object, in the present paper, to examine either 
the first effect of the cornea in rendering the rays of light 
convergent, or the power of the crystalline lens in finally 
bringing them to a focus on the retina. It is not my intention 
to investigate whether the adaptation of the eye to different 
distances is effected by alteration of the form of the lens from 
