ANIMAL BIOLOGY 



their sockets, or orbits, by means of six small muscles. 

 Their outer exposed surface is kept moist by the secretion 

 of the lachrymal glands. Normally this secretion is drained 



FIG. 218. The eye. i, lachrymal gland; 2, tear duct. 



off by the tear duct which leads from the inner angle of 

 the eye to the nasal cavity, but when the secretion is 

 unusually abundant it may overflow as tears. The eye 



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3 5 



FIG. 219. Sectiont hrough the eye. I, optic nerve; 2, vitreous body; 

 3, sclerotic; 4, choroid; 5, retina,. 6, cornea; 7, anterior chamber; 8, iris; 

 9, pupil; 10, crystalline lens. 



is nearly spherical in form and is furnished with a tough, 

 whitish, fibrous outer coat, the sclerotic, which extends 

 over all but the anterior surface where it is replaced by the 



