THE ORGANS OF SPECIAL SENSE. 



71 



point on an object must meet again in a common point 

 upon the retina, their conjugate focus. In the normal 

 eye all the rays from an object are focused on the ret- 

 ina and form upon it an image of the object which, as 

 in the camera, is inverted, because of the crossing of 

 the rays behind the cornea. Once focused on the ret- 



Fio. 26. Diagram showing the difference between (.4) emmetropic, (B) myopic 

 and (C) hypermetropic eyes. (American Text-book of Physiology.) 



ina the light traverses the various layers to the layer of 

 rods and cones, where chemical action takes place and 

 affects the little filaments of the optic nerve, by which 

 the message is carried to the brain. 



When the eye is at rest the pupil and lens are in their 

 normal condition and at such times the eye sees only 



