154 Practical Zoology. 



it. If the eye be held in the hand while trying to cut its tough 

 outer coat, the jellylike contents are easily squeezed out, ruin- 

 ing the dissection. Let the eye rest on the board all the time, and 

 after first cutting into the cornea it is not necessary nor ad- 

 visable to touch it with the fingers! When studying the lens, be 

 very careful to tip it up gently and compare its front and back 

 surfaces before removing it from the eye. 



1. Lay the eye on the board, with the cornea uppermost. 

 Hold the eye firmly with the thumb and fingers of one hand ; 

 with the thumb and forefinger of the other hand hold the blade 

 of the scalpel half an inch from its tip ; with a steady motion 

 push the blade horizontally through the cornea, near its edge. 



2. The liquid in the cavity back of the cornea is the aqueous 

 humor. 



3. Slightly enlarge the cut horizontally ; then with the forceps 

 take hold of the upper edge of the cut, and with the scissors 

 cut around the margin of the cornea and remove it. 



4. The dark membrane now exposed is the iris. Pinch the 

 eye slightly at* the sides to make the iris show more distinctly. 

 The hole in its center is the pupil. With the forceps raise the 

 edge of the iris around the margin of the pupil to see that it is 

 here unattached to the structures underneath. Observe the 

 color and markings of the iris. 



5. From one end of the pupil cut outward to the outer 

 margin of the iris ; then cut around its outer margin and re- 

 move it. Observe the color and markings of the posterior 

 surface. 



6. The body now laid bare is the crystalline lens. Touch it. 



7. Lay a piece of newspaper close to the eye, on which to 

 receive the lens, which sometimes pops out suddenly. With 

 a very sharp blade make a quick, light gash across the surface 

 of the lens to cut through the thin coat which envelops it, the lens 

 capsule. Usually the lens may be made to come out by applying 

 gentle pressure to the sides of the eye with the thumb and finger. 

 If not, enlarge the opening thus made, and carefully pry up the 



