THE EYE 113 



13. Separate the rest of the retina from the choroid 

 and observe that 



The pigment-layer generally adheres rather to the 

 choroid than to the retina. 



Apart from the pigment-layer the retina appears like 

 an expansion of the optic nerve. 



The retina is firmly attached to the choroid at the 

 or a serrata. 



DEMONSTRATIONS. 



1. Effect on the iris of stimulating the sympathetic 

 nerve. 



2. Effect of adrenaline on the iris of the frog. 



3. Muscles of the eye dissected in the head of a sheep 

 or dog. 



4. Section through centre of the eye 1 , showing the 

 position of the lens and other parts. 



1 A fresh eye is placed in a glass receptacle, e.g. a glass stopper, the 

 depth of which is half the diameter of the eye; the vessel is filled up 

 with gum, the eye arranged so that the optic nerve is horizontal; it is 

 then placed in a freezing mixture; when the eye is frozen a razor is 

 passed along the top of the vessel cutting the eye in two. 



