Mammalia. 155 



lens with the handle of the forceps, noting closely, in so doing, 

 the difference between the front and back surfaces. Lay the 

 lens on the piece of newspaper, and look through it at the letters. 

 Make a drawing of the lens as seen from the front, and as seen 

 from one side, naming the front and back surfaces. 



8. (CAUTION. In removing the strip of eye coating, as di- 

 rected below, be extremely careful not to drag the clear, jelly- 

 like vitreous humor. The strip must not be unwound, as in 

 peeling an apple, but must be left in place. The parts must be 

 lifted gently by the forceps, and the clear, jellylike mass must 

 be cut through horizontally, with the scissors.) With the scissors 

 now cut outward about one half of an inch from the edge of the 

 hole made in front of the eye, merely cutting through the outer 

 wall of the eye. Beginning at the lower end of this last cut, with 

 scissors cut through the coats of the eye, horizontally, all around 

 the eye. With forceps take hold of the upper edge of the coats 

 of the eye, and lift very gently and steadily while cutting horizon- 

 tally through the jellylike contents of the eye, in the plane of the 

 circular cut just made. Lay the part thus cut off wrong side up 

 on the board. On the inside of the strip removed there may be 

 found radiating black ridges, the ciliary processes. 



9. Carefully pick away with the forceps, and snip away with 

 the scissors, everything on the surface of the clear mass beneath. 



10. The substance filling the remainder of the eye cavity is 

 the vitreous humor. 



11. Through the vitreous humor the entrance of the optic 

 nerve may be seen with the blood tubes radiating from it. If 

 necessary, carry the dissecting board to a window to let the light 

 enter from above. 



12. The tough outer coat of the eye is the sclerotic coat. 



13. Inside the sclerotic is the dark choroid coat. 



14. The inner, nearly transparent, pinkish or whitish coat is 

 the retina. At this stage of the dissection it has probably become 

 slightly wrinkled, and the white ridges may be seen radiating from 

 the entrance of the optic nerve. 



