268 Mr. Smith's Observations on the 
rational principles explain, why people by being long ac- 
customed to view small objects obtain in time a sort of mi- 
croscopic power, if it may be so called ; that is, the muscles 
which contract the cornea will by custom increase their power 
of action, and grow stronger, like the other muscles of the 
body. Other phaenomena of vision on these principles may be 
explained. 
EXPLANATION OF THE PLATE (Tab. XXII.) 
Fig. i. represents the eye of a buzzard, blown up and dried, 
the lesser circle of the cornea suddenly rising above the scle- 
rotic coats. 
Fig. 3. is a representation of the imbricated or loricated 
appearance of the scales which cover part of the sclerotic coat 
of the eye, divested of its muscles. 
Fig. 4. shews that the scaly appearance is weaker in some 
birds than in others, according to their different modes of 
life, more so in the turkey than in the buzzard, (see fig. 3.) 
representing likewise one of the recti muscles attached to the 
scales. 
Fig. 5. the inside view of these scales in the eye of a turkey, 
the internal coat of the cornea being torn up, or separated 
from the external. 
Fig. 6 . the four recti muscles in the eye of the sheep, dis- 
sected so as to shew their fibres inserted into, and going to 
form, the outer coat of the cornea. 
Fig. 7. the four recti muscles of the eye of the turkey, 
