on Muscular Motion. 
25 
their muscular power, nor sufficiently attached to the coats of 
the eye, to alter its form by their contraction. In birds like- 
wise, the bony rim renders this impossible. 
That the axis of vision is really lengthened, and the lens 
moved forwards, for the purpose of adjusting the eye to see 
near objects, is rendered highly probable, since all the facts I 
have been able to collect seem to point out these changes; 
nor can the action of the external muscles increase the curva- 
ture of the cornea without producing them. 
If the axis of vision being lengthened was believed by some 
physiologists to produce the whole adjustment of the eye to 
see near objects ; if the crystalline lens being moved forwards 
was supposed by others to do the same thing ; and if the cor- 
nea being rendered more convex appeared at the first view 
equally to account for it ; all the three, when combined for that 
purpose, must undoubtedly be considered as sufficient to pro- 
duce the effect. 
EXPLANATION OF THE PLATE. (Tab. I.) 
Fig. 1. A side view of the cornea of the eye of a goose, to 
show the bony rim, and elastic annular ligament, in their na- 
tural situation ; a the bony rim ; b the elastic ligament. 
Fig. 2. A view of the same parts, in the eye of the great 
horned owl, to show the difference of structure ; taken from a 
dried preparation in Mr. Hunter's collection.* 
* Since this lecture was read before the Royaf Society, Sir Joseph Banks has put. 
into my hands a paper upon the anatomical structure of the eye, in which there is 
a plate, containing four views of the bony rim in the owl’s eye. The parts they re- 
MDCCXCVI. E 
