460 THE SENSORIAL FUNCTIONS. 



§ 3. Structure of the Eye. 



One of the many points of superiority which the 

 eye possesses over the ordinary camera obscura 

 is derived from its spherical shape, adapting the 

 retina to receive every portion of the images 

 produced by refraction, which are themselves 

 curved : whereas had they been received on a 

 plane surface, as they usually are in the camera 

 obscura, a considerable portion of the image 

 would have been indistinct. This spherical form 

 is preserved by means of the firm membranes 

 which protect the eye, and which are termed 

 its Coats ; and the transparent media which 

 they enclose, and which effect 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 sup- 



