CHAPTER XIV. 

 THE EYE. 



THE eye is the chief organ of sight. It is situated in the 

 orbital fossa, mentioned in the chapter on the bones of 

 the head. It is chiefly made up of several coats around 

 the outside, and in the centre by the humours of the 

 eye. On the inner side of these coats is a thin membrare called 

 the retina, which contains the branches of the optic nerve. This 

 receives the reflections of objects as they pass through the 

 humours of the eye and from which the sensation passes 

 along the optic nerve to the brain. The oblong opening seen 

 in the middle of the eye is known as the pupil. If a horse be 

 led from a dark stable into the light and the pupils of the 

 eyes watched closely, it will be noticed that they get 

 smaller; but on returning it to the stable the pupils will be 

 noticed to dilate or get larger, thus it is seen that the pupils 

 do not always remain the same size. The chief use of the 

 pupil is to gauge the sight. At the back part of the eye are 

 several muscles attached from around the eye to the bones in 

 the fossa. These muscles move the eye and assist in holding 

 it to its place. Around the front part are two movable cur- 

 tains, one above and the other below, called the eyelids, the 

 use of which is to open and close the eye, and also to protect 

 it from injuries. Around the free border of the eyelids are 

 what is known as the eyelashes, which keep foreign sub- 

 stances from falling into the eye. Situated in the inner angle 

 is what is known as the haw of the eye ; this membrane also 

 helps to protect it. In the corner of this angle is a small duct 

 or opening, through which a fluid called the tears passes 

 down into the nasal tubes, from whence it is carried down 

 through the bones of the head and emptied into the under 

 part of the nostril or nose. A small gland is situated on the 

 upper part of the eye. This gland secretes the tears which 

 lubricate the eyes. The color of the eye is generally brown, 

 but in some cases it is white. It is then called a walled eye. 



