264 ELEMENTARY PHYSIOLOGY. [XXVI. 



3. Cut away the conjunctiva and muscles, and 

 remove the fat around the optic nerve; this 

 pierces the sclerotic on the nasal side, and not in 

 the axis of the eye. 



4. Cut through the cornea close to its junction with 

 the sclerotic; the anterior chamber of the eye, 

 containing clear, limpid aqueous humour, is 

 thus laid bare. Observe the iris with its central 

 aperture through which projects the anterior 

 part of the lens. 



5. At a little distance from the cornea, cut through 

 the sclerotic, being caref ul not to cut too deeply ; 

 it will separate easily from the pigmented sub- 

 jacent choroid, except at the junction of the 

 sclerotic with the cornea, and at the entrance of 

 the optic nerve. In other places there is only a 

 loose connection, largely by means of blood- 

 vessels. Remove a strip of the sclerotic a few 

 mm. breadth stretching from the optic nerve to 

 the cornea. Note its dark inner surface, or la- 

 mina fusca ; note also in the front part of the 

 choroid, close to the cornea, the pale fibres of 

 the ciliary muscle spreading from the junction 

 of the sclerotic and cornea, backwards over the 

 choroid. 



G. Carefully pinch up the choroid about half-way 

 between the optic nerve and the cornea with a 

 fine pair of forceps, and snip it through. Un- 

 derneath it will be seen a thin membrane, the 

 retina. The pigment layer of the retina will 

 probably be torn away with the choroid. 



