THE EYE, AND THE PHENOMENA OF VISION. 349 



Fig. 282. The arrangement of tlieso 



muscles is shown in Fig. 282, 

 where the external bones of 

 the temple are supposed to bo 

 removed in order to render 

 them visible. The muscle, 1, 

 raises the ej^ehd, and is con- 

 stantly in action while we are 

 awake. During sleep, tho 

 muscle being in repose and 

 relaxed, the eye-lid falls and 

 protects the eye from the ac- 

 tion of light. The muscle, 4, 

 turns the eye upward; 5, 

 downward; 6, outward; and 

 a corresponding one on the in- 

 side, not seen in the figure, 

 turns it inward. Kos. 2 and 

 10 turn the eye round its axis. 



The eye consists essentially of four coats, or 

 membranes, called the Sclerotic coat, the 

 Choroid coat, the Cornea, and the Ketina ; 

 and these coats inclose three transparent liquids, called hu- 

 mors — the Aqueous humor, tlie Vitreous humor, and the 

 Crystalline humor, the last of which has the form of a lens. 

 Describe the The Sclcrotic coat is the external coat of the 

 Sclerotic coat, g^g^ ^^^ ^'^^ ^^^ upon ^yhich the maintenance 



of the form of the eye chiefly depends. 



It is a stronjr, toush 



Of what parts 

 does the eye 



consist ? 



membrane, and to it the 

 muscles which move the 

 eye are attached. It cov- 

 ers about four fiftlis of tho 

 external surface of the 

 eye-ball, leaving, however, 

 two circular openings, one 

 before and the other be- ^. 

 hind the eye. Its position 

 is shown at i, Fig. 283. 



The 



Cornea 



the clear, trans- 



FiG. 283. 



"What is the 



Conieii ? 



IS 



parent coat which 



