276 



THE SPECIAL SENSES 



which is called the conjunctiva, is highly sensitive, and thus 

 plays an important part in protecting the eye against the lodg- 

 ment of sand, ashes, chaff, 

 and other foreign particles 

 that are blown about in the 

 air. This sensitive mem- 

 brane will not endure the 

 presence of these particles. 

 If any dust finds access, it 

 causes a constant winking, 

 a flow of tears, and other 

 signs of irritation, until it 



FIG. 63. FRONT VIEW OF EIGHT EYE 

 (Natural Size) 

 1. The Lachrymal, or tear gland, lying be- 



is removed. 



neath the upper eyelid 



2. The Nasal Duct is shown by the dotted 

 line. The * marks the orifice in the lower lid 



The central black spot is the pupil; sur- 

 rounding it is the iris; and the triangular 

 white spaces are the visible portion of the 

 sclerotic 



(Read Note 8.) 



55. The long, silky eye- 

 lashes, which garnish the 

 edges of the lids, act like a 

 sieve to prevent the entry of 

 dust and other irritants ; and 

 together with the lids, they 



regulate the amount of light which is permitted to enter the 

 eye, so that it is shielded from a sudden flood or glare of light. 

 The little points seen in the figure just within the line of the 

 lashes, especially on the lower lid, represent the mouths of 

 numerous little sebaceous glands (Fig. 64, D, D), such as are 

 always found in the neighborhood of hairs. These glands sup- 

 ply a thick, oily material which greases the edges of the lids 

 and prevents their adhering together, and likewise prevents 

 the overflow of the tears upon the cheek. 



8. How to Remove Foreign Bodies from the Eye. "Lay your 

 finger on the cheek, and draw the lower lid gently down, while the person 

 looks as much upward as possible, and we shall see about the whole ex- 

 tent of the lower portion of the conjunctiva, and thus, if any foreign 

 substance is there, it will be readily detected, and easily wiped away with 

 a folded soft rag or handkerchief. Both lids have a piece of cartilage in 

 them to stiffen them, like pasteboard, and keep them fitting close to the 

 eyeball. The upper portion of this conjunctival sac can only be seen by 

 turning over the upper lid. The way to do this is to let the person look 



55. The eyelashes ? The little points within the line of the lashes ? Of what use are 

 these glands ? 



