VISION. 



461 



port it requires for the performance of its deli- 

 cate functions. It is perforated behind by the 

 optic nerve (o), which passes onwards to be ex- 

 panded into the retina (r). The sclerotica does 

 not extend farther than about four-fifths of the 

 globe of the eye ; its place in front being sup- 

 plied by a transparent convex membrane (c). 



called the Cornea, wliich is more prominent than 

 the rest of the eye-ball. A line passing through 

 the centre of the cornea and the centre of the 

 globe of the eye is called the axis of the eye. 

 The Sclerotica is lined internally by the Choroid 

 coat (x), which is chiefly made up of a tissue of 



