DISEASES OF THE EYE, ETC. 348 



nerve between the brain and the ball of the eye, and becomes attached 

 upon the external face of the sclerotic tunic. When this muscle con- 

 tracts, it draws the globe back into the orbit, away from the light. 

 The superior, inferior, external, and internal recti or straight muscles 

 are attached to the back part of the orbital sheath, and spread forward 

 in four bundles over the globe of the eye, where they become inserted 

 by a fibrous expansion into the sclerotic at the margin of the cornea. 

 "When they act singly they turn the globe either Upward, downward, 

 inward, or outward. The great oblique, by its action, pivots the eye 

 inward and upward in the orbit. The small oblique turns the eye 

 outward and downward. 



The eyelids are two movable curtains, superior and inferior, which 

 cover and protect the eye in front. They are attached to the circum- 

 ference of the orbit, and have a convex external face formed by the 

 skin and a concave internal face molded on the anterior surface of 

 the eye, and are lined by the conjunctiva, which is reflected above and 

 below on the eyeball. The border of each- lid is slightly beveled on the 

 inner side, and shows the openings of the Meibomian glands. These 

 glands secrete an unctuous fluid, which is thrown out on the border 

 of the lids, the function of which is to facilitate their movements and 

 enable them to retain the tears in the ocular cavity. The eyelid is 

 composed of a fibrous inner membrane ending in a stiff arch near the 

 border, a muscle to close the lid, another to open it, the skin externally, 

 and the conjunctival mucous membrane internally. The border of 

 each lid is covered and protected by long hairs, to prevent floating 

 ' particles of matter in the atmosphere gaining entrance to the eye. 



The membrana nictitans, which is also named the third eyelid, wink- 

 ing eyelid, haw, etc. , is placed at the inner angle of the eye, whence 

 it extends over the eyeball to relieve it from foreign bodies which may 

 fall upon it. It has for its framework a fibro-cartilage, irregular in 

 shape, thick, and nearly prismatic at its base, and thin anteriorly 

 where it is covered by the conjunctiva; behind, it is loosely attached 

 to a fatty cushion. 



The lachrymal gland is situated between the orbital process and the 

 upper part of the eyeball. It secretes the tears destined to lubricate 

 the anterior surface of the eye. This fluid escapes upon the organ at 

 the outer angle of the lids, and is carried between them and the eye- 

 ball toward the inner angle. 



The caruncula lachrymalis is a small round body, frequently entirely 

 or partially black, situated in the inner angle of the eye, and is designed 

 to direct the tears toward the puncta lachrymalia. 



The puncta lachrymalia are two little openings, situated one in each 

 eyelid, a short distance from the inner corner, which admit the tears 

 into the lachrymal ducts leading to the lachrymal canal, from whence 

 they are emptied into the nasal passages. 



