MUSCLES AND PARTS CONNECTED WITH THE EYE. 
203 
beautifully proves design in the formation and adaptation of 
the animal. The eyelashes should on no account whatever 
be cut, as they have a most important office to fill, not only 
preventing the eye from being injured by dazzling light, but 
also protecting it from the intrusion of insects. 
The horse is destitute of eyebrows, but in their stead he 
is provided with a number of scattered bristly hairs, as also 
a projecting fold of the upper eyelid, which answers the 
same purpose. Some persons are so foolish as to cut off 
these hairs, and have absurdly attributed them to weakness. 
The under eyelid also is furnished with projecting bristly 
hairs, which are so sensitive that they give immediate warn¬ 
ing to the animal of the approach of any insect or other 
object which might injure the eye, and he naturally closes 
the eyelid instantaneously. Ignorant grooms sometimes 
denude horses of these admirable premonitory feelers. 
The power of this muscle is so great, that it has been 
ascertained to exert a force equal to twenty pounds, and 
in consequence the operation for cataract is rendered nearly 
impossible. It will thus be seen that these muscles are 
admirable substitutes for the want of hands, in protecting 
the eyes against the intrusion of things that would injure 
them. They are also partially separated into four divisions, 
and by this means assist the straight muscles in turning 
the eye. 
These muscles perform another important office in altering 
the focus of the eye to accommode itself to the examination 
of distant or near objects. (See c and 6, fig. 5.) The 
straight and retractor muscles draw back the eye, and 
forces it upon the substance, and thus in a slight degree 
flattens it, brings it nearer the retina or mirror, and adapts 
the eye to the observation of distant objects. 
But as these muscles are chiefly employed in supporting 
