258 Life and Health 



Thus the beauty of the internal mechanism of the eye 

 has its fitting complement in the precision, delicacy, and 

 range of movement conferred upon it by its muscles. 



402. StraSbismus. When, for any cause, the coordi- 

 nation is faulty, "cross-eye," technically called strabismus, 

 is produced. Thus, if the internal rectus is shortened, the 

 eye turns in ; if the external rectus, the eye turns out, 

 producing what is known as " wall-eye." 

 \ 403. The Eyelids. The eyelids, two in number, move over 

 the front of the eyeball and protect it from injury. They 

 consist of folds of skin lined with mucous membrane, kept in 

 shape by a layer of fibrous material. Near the inner surface 

 of the lids is a row of glands, known as the Meibomian 

 glands, which open on the free edges of each lid (Fig. 137). 



The inner lining membrane of the eyelids is known as 

 the conjunctiva ; it is richly supplied with blood vessels and 

 nerves. After lining the lids it is reflected on to the eye- 

 balls. Jt is this membrane which is occasionally inflamed 

 from taking cold. 



\ 404. The Eyelashes and Eyebrows. The free edges of 

 the lids are bordered with two or more rows of hairs called 

 the eyelashes, which serve to protect the eyes from dust, 

 and to a certain extent to shade them. Their loss gives a 

 peculiar, unsightly look to the face. 



The upper border of the orbit is provided with a fringe of 

 short, stiff hairs, the eyebrows. They help to shade the eyes 

 from excessive light, and to protect the eyelids from 

 perspiration, which would otherwise cause discomfort. 

 > 405. The Lachrymal Apparatus. Nature provides a spe- 

 cial secretion, the tears, to moisten and protect the eye. 

 The apparatus producing this secretion consists of the 

 lachrymal or tear gland and lachrymal canals or tear passages 

 (Figs. 135 and 137). 



