THE EYE 91 



i. The capsule of the lens is an elastic transparent 

 membrane holding the lens in its place. 



ii. The suspensory ligament of the lens, or zonule of 

 Zinn, is the outer margin of the capsule of the 

 lens: it is marked with radiating folds into 

 which the ciliary processes fit. 



iii. The cut edges of the retina and choroid should be 

 recognised. 



7. Remove the lens from its capsule; note its shape, more 

 convex behind than in front : harden it with spirit, or by boiling 

 for a few minutes in water. 



8. Remove the vitreous humour from the posterior half of the 

 eye : note the following points : 



i. The retina is a delicate pulpy membrane between 

 the vitreous humour and the choroid. 



ii. The blind spot is the point of entrance of the optic 

 nerve: the retina adheres firmly to this spot, 

 though it can be readily separated from the 

 choroid at all other parts. 



iii. The retinal vessels enter with the optic nerve, and 

 radiate from the blind spot. 



0. Histology of the Eye. 



1. The Choroid. Spread a, small piece of fresh choroid on a 

 slide in normal salt solution; examine with low and high powers. 



i. The choroid is a network of bloodvessels thickly 

 invested by pigment cells. 



ii. The pigment cells are irregularly branched, with 

 clear nuclei. 



2. The Lens. Tease in glycerine a small piece of lens, 

 hardened by boiling ; examine with low and high powers : note : 



i. The laminated character of the lens as a whole. 



ii. The elongated epithelial cells of which the lens is 

 composed. 



iii. The serrated edges of many of the cells. 



