THE SENSES 



231 



IRIS 



L5NS 



the iris and the front of the eye is a watery-like material, 

 the aqueous humor, which keeps the front of the eye ex- 

 tended into its rounded 

 form. Back of the lens 

 is a thick, transparent, 

 jelly-like material, the 

 vitreous humor, which 

 holds the retina extended 

 and keeps the eye from 

 collapsing. 



Instead of moving the 

 retina back and forth to 

 focus a picture, as is done CROSS SECTION OF THE HUMAN EYE. 



with the ground -glass The pupil is the opening between the 

 , , . upper and lower parts of the iris as 



plate m a camera, the shown in the figure, 



eye lens is capable of 



adjusting itself so as to focus objects which are at different 

 distances. Leading back to the brain from the retina, is 

 the optic nerve, which carries the impressions made on the 



retina to the brain where 

 they are interpreted into 

 the sensation of sight. 



This rough comparison 

 is by no means a descrip- 

 tion of the eye, for it is a 

 most complex and wonder- 

 ful organ, vastly superior 

 in construction to a 

 camera. A technical de- 

 scription would, however, 

 be out of place here. 



The ear, which is the 

 sound transmitter, consists of the outer ear, which is so 

 arranged as to catch the sound waves and converge them 



CROSS SECTION OF THE HUMAN EAR. 



