228 ANATOMY FOR NUKSES. [CHAP. XIX. 



Befr acting media. 1. Aqueous. 



2. Crystalline lens and capsule. 



3. Vitreous. 



The sclerotic (derived from a Greek word signifying hard) 

 covers the posterior five-sixths of the eyeball. It is composed 

 of a firm, unyielding, fibrous membrane, thicker behind than in 

 front, and serves to protect the delicate structures contained 



FIG. 131. THE LEFT EYEBALL IN HORIZONTAL SECTION FROM BEFORE BACK. 

 1, sclerotic; 2, junction of sclerotic and cornea; 3, cornea; 4, 5, conjunctival mem- 

 brane ; 7, ciliary muscle ; 10, choroid ; 11, 13, ciliary processes ; 14, iris ; 15, retina ; 

 16, optic nerve; 17, artery entering retina; 18, fovea centralis; 19, region where 

 sensory part of retina ends ; 26, 27, 28, are placed on the lens ; 28, suspensory liga- 

 ment placed around lens; 29, vitreous humour ; 30, aqueous humour in anterior 

 chamber. 



within it. It is opaque, white and smooth externally, and 

 behind is pierced by the optic nerve. Internally it is stained 

 brown where it comes in contact with the choroid coat. The 

 cornea (derived from Latin cornu, horn, and therefore also sig- 

 nifying hard) covers the anterior sixth of the eyeball. It is 

 directly continuous with the sclerotic coat, which, however, 

 overlaps it slightly above and below, as a watch-crystal is over- 

 lapped by the case into which it is fitted. The cornea, like the 



