568 ANIMAL PHYSIOLOGY. 
follows: The lens is naturally very elastic and is kept in a par- 
tially compressed condition by its capsule, to which is attached 
the suspensory ligament which has a posterior attachment to 
the choroid and ciliary processes. When the ciliary muscle, 
Fie. 412.—Illustrates mechanism of accommodation (after Fick). The left side depicts. the 
relation of parts during the passive condition of the eye (negative accommodation, or 
accommodation for long distances); the right side, that for near objects. 
which operates from a fixed point the corneo-sclerotic junction, 
pulls upon the choroid, etc., it relaxes the suspensory ligament; 
hence the lens, not being pressed upon in front as it is from 
behind by the vitreous humor (invested by its hyaloid mem- 
brane), is free to bulge and so increase its refractive power. 
The nearer an object approaches the eye, the greater the diver- 
gence of the rays of light proceeding from it, and hence the 
necessity for greater focusing power in the lens. 
If a person be observed closely when looking from a remote 
to a near object, it may be noticed that the eyes turn inward— 
i.e., the visual axes converge and the pupils contract. These 
are not, however, essential in the sense in which the changes 
in the lens are; for, as before stated, in the absence of the lens 
distinct vision is quite impossible. Were additional evidence 
necessary to show that accommodation is effected as described, 
it might be stated that by stimulation of the lenticular gan- 
glion the ciliary muscle may in an animal thus experimented 
upon be shown to contract, the choroid to be drawn forward, 
and the anterior convexity of the lens to be increased. Vaso- 
motor changes or alterations in the size of the iris, if they have 
any effect upon the lens at all, must play a very unimportant 
part. The movements of the iris do, however, serve an impor- 
tant purpose, and to that subject we now turn. 
