326 



THE SENSORIAL FUNCTIONS. 



the convergence of the rays, are termed the Humours of 

 the Eye. There are in this organ three principal coats, and 

 three humours, composing altogether what is called the 

 Globe of the Eye. Fig. 415, which gives an enlarged view 

 of a horizontal section of the right eye, exhibits distinctly 

 all these parts. 



The outermost coat (s,) which is termed the Sclerotica, is 

 exceedingly firm and dense, and gives to the globe of the 

 eye the mechanical support it requires for the performance 

 of its delicate functions. It is perforated behind by the op- 

 tic nerve (o,) which passes onwards to be expanded into the 

 retina (n.) 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- 



415 



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 

 g ye. The Sclerotica is lined internally by the Choroid coat 



