224 PHYSIOLOGY. 



to it, through which the light, passing, falls upon a screen 

 behind, forming an inverted image of the object represented, 

 we say at once here is design ! But this instrument also is 

 copied from the human eye ! 



Questions. What is said of the sense of sight ? What arc the coats 

 of the eye ? Describe the scelerotic ? the choroid ? What is the pig- 

 mentum nigrum ? Is it ever absent ? Describe the retina ? Illustrate the 

 minuteness with which objects are painted on it ? Describe the cornea ? 

 the ciliary ligament ? What is said of these tunics in the lower 

 order of animals ? What is the iris ? How does it contract and di- 

 late ? Are the muscles ever under the control of the will ? What is 

 said of the iris among the lower animals ? Describe the ciliary pro- 

 cesses ? What are the humours of the eye ? Describe the aqueous ? 

 the crystalline ? the vitreous ? Explain some of the laws of vision ? 

 What is a lens ? How many, and what kinds of lenses are there ? 

 What effect on light has a concave ? a convex ? a plain lens ? Illus- 

 trate this by the humours of the eye. Are images erect on the retina ? 

 Where do the rays cross ? How do you explain why we do not see 

 objects inverted ? Why do we not see objects double ? Why do riv- 

 ers appear shallower than they are? To what is short-sightedness 

 owing ? How may it be corrected ? What is long-sightedness ? What 

 is the remedy ? Are there persons who cannot distinguish colours ? 

 To what is this owing ? What is said of compound eyes ? How 

 many muscles are there to move the eye 1 Describe them ; the recti ; 

 the oblique. What are the defences of the eye ? Describe the orbit ; 

 the eyelids ; the muscles of the lids. Are they voluntary muscles ? 

 How are objects carried into the angle of the eye ? What is the use 

 of eyelashes ? of eyebrows ? How are the tears secreted ? How , 

 carried out of the eye ? What has led to a belief in supernatural ap- 

 pearances ? 



