XXVI.] THE EYE. 271 



6. The cross sections of the bundles of plain 

 muscular fibres forming the sphincter pu- 

 pillse near the edge of the pupil, and lying 

 just above the pigment-layer. 



c. The body of the iris, consisting of blood- 

 vessels united together by a loose connective 

 tissue in which branched pigment-cells are 

 conspicuous. Near the anterior surface is a 

 denser layer, the so-called anterior limiting 

 membrane. The radial muscular fibres (di- 

 lator) may (with difficulty) be seen near the 

 posterior surface. 



8. Take the iris from a white rat's or an albino 

 rabbit's eye which has been, preserved in 

 Miiller's fluid. Cut out a piece from the free 

 edge to the attachment, stain with haema- 

 toxylin, clear, and mount in Canada balsam 

 with the posterior surface uppermost. Observe 

 the arrangement of the sphincter and dilator 

 muscles. 



Retina. 



9. Cut away the anterior half of the eye of a mam- 

 mal immediately after death : avoid dragging 

 the vitreous humour that the retina may not be 

 displaced. Place the posterior half in potassium 

 bichromate 2 p.c. or in Miiller's fluid for a week, 

 changing the fluid once or twice. After treatment 

 with alcohol remove the retina carefully, carrying 

 with it if possible the pigment-layer. Stain a small 

 piece with ha3matoxylin, imbed it in spermaceti 



