336 
OBSERVATIONS ON SOUNDNESS ” 
By R. II. Dyer, M.R.C.V.S., Waterford. 
(^Continuedfrom p. 264.) 
The visual organ being required to take cognisance of 
every surrounding object, its size, colour, shape, and form, 
during the night as well as during the day, it is necessary that 
the individual so circumstanced should have the power of 
moving that organ in as many directions as may be requisite. 
This is done by means of its muscles. Man is not endowed 
with the same power as the horse is with regard to the 
movements of the globe of the eye. Man has no retractor 
muscle; he does not require it: the horse has, he not being 
possessed of hands. It may well be said, that this muscle (or 
that which the muscle influences) is to the horse what a hand 
is to man. It is necessary, therefore, that each and every 
muscle of the globe of the eye, and its appendages, should be 
well developed, or in all probability sight will be impaired to 
a certain extent. We frequently hear of this muscle of the 
neck and that muscle of the leg being but poorly developed, 
but 1 have never heard it remarked that the muscles of the 
eye are in any way at fault, except in man, in that peculiar 
affection termed strabismus. I have never seen this in the 
horse. It is a subject comparative anatomists would do well 
to turn their attention to. It has before been said, that some 
large horses have small eyes, and vice versa ; but it has not to 
my mind been fully and satisfactorily explained. Our atten¬ 
tion has been directed almost solely to the lens. When we 
take into consideration the many and varied hues of light the 
horse has to take cognisance of, in daylight as well as in the 
dark, we need not wonder at his making some woeful mis¬ 
takes when the'visual organ is out of order; and in addition 
to this, he has the ignorance of his, sometimes, ill tempered 
master to influence or to puzzle him in his difficulties. Too 
much importance cannot be attached to the development of 
muscle in connection with the eye of the horse. 
The direction light travels is always in straight lines, if the 
medium through which it passes is of uniform density. When 
a ray passes from a rarer to a denser medium, it is refracted 
or bent towards the perpendicular; when a ray of light 
passes from a denser to a rarer medium, it will be refracted 
from the perpendicular; when rays proceed from several 
