62 
Dr. Young’s Lecture 
From the experiments related, it appears to be highly im- 
probable that any material change in the length of the axis 
actually takes place; and it is almost impossible to conceive by 
what power such a change could be effected. The straight 
muscles, with the adipose substance lying under them, would 
certainly, when acting independently of the socket, tend to 
flatten the eye : for, since their contraction would necessarily 
lessen the circumference or superficies of the mass that they 
contain, and round off all its prominences, their attachment 
about the nerve and the anterior part of the eye must therefore 
be brought nearer together. (Plate V. Fig. 21, 22.) Dr. 
Olbers compares the muscles and the eye to a cone, of which 
the sides are protruded, and would by contraction be brought 
into a straight line. But this would require a force to preserve 
the cornea as a fixed point, at a given distance from the origin 
of the muscles ; a force which certainly does not exist. In the 
natural situation of the visual axis, the orbit being conical, the 
eye might be somewhat lengthened, although irregularly, by 
being forced further into it ; but, when turned towards either 
side, the same action would rather shorten its axis ; nor is there 
any thing about the human eye that could supply its place. 
In quadrupeds, the oblique muscles are wider than in man; 
and in many situations might assist in the effect. Indeed a 
portion of the orbicular muscle of the globe is attached so near 
to the nerve, that it might also co-operate in the action : and I 
have no reason to doubt the accuracy of Dr. Olbers, who 
states, that he effected a considerable elongation, by tying threads 
to the muscles, in the eyes of hogs and of calves ; yet he does 
not say in what position the axis was fixed ; and the flaccidity 
of the eye after death might render such a change very easy as 
