i Mr. Young's Observations on Vision. 
Although a strong light and close examination are re- 
quired, in order to see the fibres of the crystalline in its intire 
state, yet their direction may be demonstrated, and their at- 
tachment shewn, without much difficulty. In a dead eye the 
tendons are discernible through the capsule, and sometimes 
the anterior ones even through the cornea and aqueous hu- 
mour. When the crystalline falls, it very frequently sepa- 
rates as far as the centre into three portions, each having a 
tendon in its middle. If it be carefully stripped of its cap- 
sule, and the smart blast of a fine blow-pipe be applied close 
to its surface in different parts, it will be found to crack ex- 
actly in the direction of the fibres above described, and all 
these cracks will be stopped as soon as they reach either of 
the tendons. The application of a little ink to the crystalline 
is of great use in shewing the course of the fibres. 
When first I observed the structure of the crystalline, I 
was not aware that its muscularity had ever been suspected. 
We have, however, seen that Descartes supposed it to be of 
this nature ; but he seems to think that the accommodation of 
the eye to a small distance is principally performed by the 
elongation of the eye's axis. Indeed as a bell shakes a 
steeple, so must the coats of the eye be affected by any change 
in the crystalline ; but the effect of this will be very incon- 
siderable ; yet, as far as it does take place, it will co-operate 
with the other change. 
But the laborious and accurate Leeuwenhoek, by the help 
of his powerful microscopes, has described the course of the 
fibres of the crystalline, in a variety of animals ; and he has 
even gone so far as to call it a muscle * ; but no one has pur- 
* Now if the cristaline humour (which I have sometimes called the crist. muscle) 
