THE SCLEROTIC. 



The sclerotic consists of bundles of fibrous tissue crossing each other in all directions in 

 the plane of the membrane. These bundles become continuous with the substantia propria 

 of the cornea at its margin. Mixed with them is a small quantity of elastic tissue. Sections 

 may be made from any eye which has been hardened in Miiller's fluid, or chromic acid and 

 spirit fluid. Stain the sections with logwood and mount them in dammar. 



V/ 



THE CRYSTALLINE LENS. 



PREPARATION, (a) Boiling. Boil the lens of a fish e.g. cod for a few mimrtcs, until it 

 becomes white. Peel off the outer softer part of the lens, and tease a little of the deeper, less 

 brittle part, in Farrant's solution. 



(<5) Glycerine and Nitric Acid Flnid. Place the eyeball of a frog, or the lens of any other 

 animal, in the above fluid (p. xxxiv) for twenty-four hours, and then in water for the same time. 

 This dissolves all 4he cement, and renders the lens-fibres so tough that they do not break 

 readily when they are teased. Tease a small piece in glycerine as above. 



Make a 'similar preparation of the lens of a dog, cat, or rabbit, and note that the lens-fibres 

 in the case of these animals are not nearly so markedly serrated (PI. XXV, Fig. 4). 



EXAMINATION (H). Observe the lens-fibres of a codfish. They are long, narrow bands, 

 with well-marked teeth or serrations along their narrow margins, the teeth of contiguous 

 fibres dovetailing with one another (PI. XXV, Fig. 5). 



(c) Potassic Bichromate. Transverse sections ought to be made across a lens hardened 

 in one per cent, potassic bichromate solution for a week. Mount them in Farrant's solution. 

 They are very apt, however, to fall to pieces. The fibres are hexagons when seen in transverse 

 section. 



The capsule of the lens, and the layer of epithelium lining it, are easily obtained from the eye 

 of a frog. 



The arrangement of the lens-fibres is easily made out in sections of a foetal eye. 



THE CHOROID. 



Sections may be made through the coats of the eyeball of an ox, hardened in chromic acid 

 and spirit mixture, to include the sclerotic and the choroid. It consists of bundles of connec- 

 tive tissue, with some elastic fibres, many blood-vessels and branched pigment-cells. The 

 layer of hexagonal pigment-cells occurring on its inner surface is now recognised as belonging 

 to the retina (PI. XXV., Fig. 7). 



Pigment-Cells of the Choroid. PB-EPARATION. From the eye of an ox, hardened as de- 

 scribed for the ciliary muscle, remove the retina. Scrape off a little of the dark pigment-layer 

 which adheres to the sclerotic, and diffuse or spread it out in glycerine. Cover. 



EXAMINATION (H). Observe the branched flattened cells, like branched connective-tissue 



