412 



THE SENSORIAL FUNCTIONS. 



(o), which passes onwards to be expanded 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 supplied by a transparent 

 convex membrane (c), called the Cornea, which 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 blood-vessels, for supplying nourishment 

 to the eye. It has on its inner surface a layer of a 

 dark coloured viscid secretion, known by the name 

 of the Pigmentum nigrum, or black pigment. Its 

 use is to absorb all the light which may happen to 

 be irregularly scattered through the eye, in conse- 

 quence of reflection from different quarters ; and it 

 serves, therefore, the same purpose as the black 



