Chapter 2 



A TYPICAL VERTEBRATE EYE: THE HUMAN 



(A) Structures and their Functions 



The human eye will serve admirably as an introduction to vertebrate 

 ocular morphology and physiology, for it is fairly well generalized and 

 presents no bizarre features. In the ensuing discussion, fine structural 

 and terminological details will be given only where they are important 

 for an understanding of the workings of the eye. Any detailed descrip- 



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V///////////////////////77, 



Fig. 2 — Comparison of eye and camera. 



Parts which correspond in function bear similar numbers. /- retina = film, on curved track; 

 2a- cornea = front element of lens; 2h- crystalline lens = rear element of lens; j- iris :z dia- 

 phragm between lens elements; 4- pigment of chorioid coat = flat black paint; 5- eyelids = 

 roller-blind shutter. 



tion of the human retina will be omitted here, since a general treatment 

 of the vertebrate retina is given in Chapter 3. The reader who wishes to 

 learn the histology of the human eye for its own sake will of course study 

 actual preparations and a textbook of microscopic anatomy. 



The Eye a 'Camera' — It is almost a cUche to say that the eye is built 

 like a camera (Fig. 2) . In each there is a sensitive screen (retina = film 

 or plate) on which an inverted image is formed by a lens (corneas- 

 crystalline lens = lens). One device (lids = shutter) can exclude light, 

 which when admitted by it is regulated in amount by a variable aperture 

 (pupil = diaphragm aperture). The interior is darkened (chorioid pig- 

 ment = dead black paint) so that internal reflections will not blur or 



