10 
Mr. Home's Lecture 
than that of a change in the cornea, as that substance is pos- 
sessed of the same refractive power with the surrounding fluid. 
To avoid confusion in so extensive a field of inquiry, I shall 
separately consider the peculiarities in the eyes of these diffe- 
rent classes of animals, so far as they appear to be concerned 
in producing the adjustment to different distances. 
Quadrupeds have three modes of procuring their food ; one 
by their fore-paws only, which they use like hands, as all the 
monkey tribe ; the second, by their fore-paws and mouths, as 
the lion, and cat tribe ; the third, by the mouth only, as all 
ruminating animals. These three different modes require the 
food being brought to different distances from the eye ; and 
it is curious, that the muscles of the eye are different in all the 
three tribes. 
In the monkey tribe, the muscles of the eye are exactly the 
same as in the human. In the lion tribe, they are double in 
number, and the four intermediate muscles are lost in the scle- 
rotic coat, at a greater distance from the cornea than the 
others. In the ruminating tribe, there are four muscles, as in 
the human eye ; but there is also a muscle surrounding the 
eyeball, attached to the bottom of the orbit, round the hole 
through which the optic nerve passes, and lost upon the scle- 
rotic coat immediately before the broadest diameter of the 
globe of the eye ; the upper portion of this muscle is rather 
the longest, its insertion being nearly in a circular line at right 
angles to the axis of vision, but not to the axis of the eye from 
the entrance of the optic nerve. 
In quadrupeds in general, the ball of the eye is broader in 
proportion to its depth, than in the human subject ; in the bull 
