XXIX] EYE 223 



4. Section through the centre of a lens at right 

 angles to its short axis. Observe the cross sections of 



o 



the fibres, and their junctional lines. 



5. Place the lens of a rabbit or rat in osmic acid '25 p.c. for 

 about three hours ; it will swell up somewhat, and the outer 

 coat becomes jelly-like and easily torn ; to obviate this, place it 

 in gold chloride -25 p.c. for a minute or less ; then tear off as 

 long a strip as possible of the outer coat, and tease out in water. 

 Observe the long band-like fibres with serrated edges usually 

 adhering together in layers but in some cases isolated. 



In some of the fibres a nucleus will be seen ; when the fibres 

 form a layer, the nuclei appear as an irregular band running 

 across it. 



6. Make a moist film preparation of, and fix with alcohol, the 

 iris of a white rat with the posterior surface of the iris upper- 

 most ; stain with haematoxylin. Observe the arrangement of 

 the sphincter muscle. 



7. Retina. Section through posterior part of the 

 eye of a mammal (Flemming's fluid or potassium 

 bichromate 2 p.c.; stained in bulk, cut in paraffin). 

 Observe 



(i) The inner limiting membrane showing as a 

 thin line. 



(ii) The layer of optic nerve fibres, thin, and 

 inconspicuous ; the fibres are without medulla, a small 

 bundle of fibres may be seen here and there, dipping 

 towards the next layer. 



(iii) The ganglionic layer, consisting of a single 

 layer of nerve-cells with conspicuous nuclei. 



(iv) The inner molecular layer, appearing as 

 very close plexus of fine fibrils. 



(v) The inner nuclear layer, showing two to 



