48 Practicum VII. The Lens. 



29. The Lens. With the scissors cut the capsule of the vitreum 

 and note, imbedded in the mass, the CRYSTALLINE LENS, already seen 

 through the pupil ( 19). Continuing to use the scissors very carefully 

 detach the entire vitreum from the lens ; the capsule of the former is so 

 closely connected with that of the latter that there will be danger of dis- 

 placing the lens. 



a. The lens is naturally clear like glass. The condition called cataract is due to 

 opacity such as in the preserved eye is caused by the alcohol. 



b. If the lens is torn apart with the nails it will be found to separate into concentric 

 layers somewhat like those of an onion ; the central portion may be still transparent. 



30. The CAPSULE OF THE LENS is really very firm ; the two layers 

 from the cephalic and caudal faces unite near the margin to form the 

 SUSPENSORY LIGAMENT ; this is attached at its periphery, and is relaxed 

 by the contraction of the ciliary muscle so as to permit the lens to become 

 more convex ; this is explained in the lectures under the head of Accom- 

 modation. The ligament is well shown in a preparation (No. 2969) of 

 the dog's eye, made by Dr. Fish. 



a. After the removal of the lens a drawing should be made. 



31. The natural conditions of the transparent mediums of the eye 

 can hardly be appreciated from alcoholic specimens, and fresh eyes should 

 be examined. Sections should also be made in the other two planes, i. e., 

 medisections and loneisections. 



