356 DISEASES OF CATTLE. 



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

 the external face of the sclerotic tunic. When this muscle contracts, 

 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 out- 

 ward and downward. 



The eyelids are two inoveable 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 Meiboinian 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 conjunctiva! 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 

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

 ball towards 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 towards the puncta lachrymalia. 



Thepuncta 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 lacrymal canal, from whence 

 they are emptied into the nasal passages. 



