THE EYE AND VISION. 115 



I. With forceps, carefully lift the chore-id coat about 

 halfway between the optic nerve and the cornea and cut 

 through it. Beneath it the retina, a thin membrane, will 

 be seen. The pigment layer of the retina will probably 

 be torn away with the choroid. 



m. The vitreous humor, which occupies the posterior cav- 

 ity of the eye, may be seen by tearing away a piece of the 

 retina. What are its characteristics ? 



n. Hold the eye so that the cornea is underneath. Look 

 through the vitreous humor and see the longitudinal folds 

 of the choroid coat. These are the ciliary processes. 



o. The ora serrata is the uneven line at the level of the 

 commencement of the ciliary processes. The retina ceases 

 along this line. 



p. Turn the eye with the iris uppermost and cut away 

 the thin edge of the iris. Find the lens. Make a slit in 

 the membrane over the lens and remove it from its capsule. 

 Find how far the lens capsule extends. How is it held 

 in place? 



q. Study the lens. 



1. Its shape, size, and transparency. 



2. Are its two faces alike ? 



3. Lay the lens over some writing and notice the 



result. 



4. Place the lens in a 1 per cent solution of potas- 



sium bichromate, and study the structure at 

 the end of a week. 



r. The blind spot is the place where the optic nerve joins 

 the retina. It may be found by removing the posterior 

 half of the eye. 



