8 
Mr. Home's Lecture 
straight muscles is the most advantageous that could be ima- 
gined for that purpose. 
This lateral pressure will not only elongate the eye, and 
increase the convexity of the cornea, but it will produce an 
effect upon the crystalline lens and ciliary processes, pushing 
them forward in the same proportion as the cornea is stretched. 
This is necessary for two reasons ; viz. to preserve the cavity 
containing the aqueous humour always of the same size, and to 
keep the cornea and lens at the same distance from each other. 
The ciliary processes, as they form a complete septum between 
the vitreous and aqueous humours, must be moved forward, 
together with the lens, when the cornea is rendered more con- 
vex, and when the cornea recovers itself they are thrown back 
into their former situation. In order to effect this with the 
nicety that is required, the ciliary processes are probably pos- 
sessed of a muscular- power. 
That the ciliary processes are muscular is a very generally 
received opinion, and in the course of this lecture I shall ad- 
duce some facts in favour of it ; they will also tend to confirm 
the opinion of these processes being a sling, in which the lens 
is suspended, and rendered capable of a small degree of motion. 
The result of this inquiry, which has not been confined to 
the support of any particular theory, but carried on with the 
sole view of discovering the truth, appears to be, that the ad- 
justment of the eye is produced by three different changes in 
that organ : an increase of curvature in the cornea, an elonga- 
tion of the axis of vision, and a motion of the crystalline lens. 
These changes in a great measure depend upon the contrac- 
tion of the four straight muscles of the eye. 
Mr. Ramsden has been good enough to make a computa- 
