318 



THE SPECIAL SENSES 



THE EYE . 



(continued) 



Coats 



Lens 



Chambers 



Optics 



Outer 



f Sclerotic 



[ Cornea 



Choroid 



Middle 



Iris 



Retina . 



< Tough, fibrous, 



opaque. 

 f Transparent. 

 I Covers the front cen- 

 tral portion of the 

 I eye. 



Contains black pig- 

 ment. 



Terminates in front 

 by the ciliary 

 processes. 

 A circular perforated 



diaphragm. 

 Aperture called the 



pupil. 



Pupil contracted by 

 circular muscular 

 fibres ; and 

 Dilated by radial 



fibres. 



j Nervous structures. 

 1 Connective tissue. 



C Aqueous 



I Vitreous 



Interior . 



Situated just behind the iris. 

 Double convex. Elastic. 

 Back surface more convex than the front. 

 Enclosed in a capsule. 



Held by the suspensory ligament at its circum- 

 ference. 



Ligament relaxed by the contraction of the 

 ciliary muscle. 



j Between the iris and the cornea. 



' Contains a watery fluid. 



f Includes the greater portion of 

 the ball. 



1 Contains a transparent jelly-like 



[ substance. 

 The eye a camera obscura or dark chamber. 

 Rays of light converge as they enter the cornea. 

 Convergence increased by the lens. 

 Image (inverted) falls on the retina. 



< Cornea or lens too convex. 



1 Eemedy wear concave glasses. 



j Cornea or lens too flat. 



( Remedy wear convex glasses. 



j At entrance of optic nerve. 



1 Totally insensitive to light. 



r T V of an inch outside the blind 

 spot. 



I Marked by a slight depression. 



[ Most sensitive part of the retina. 

 Retina retains impressions for about | of a sec- 

 ond after its exciting cause ceases. 



Short-sight . 

 Long-sight . 

 Blind spot . 



Yellow spot 



