258 THE ESSENTIALS OF HISTOLOGY. 



of the nerve-fibres and their termination amongst the epithelium-cells as 

 shown in chloride of gold preparations have been already studied (Lesson 

 XXL). 



5. Mount in Canada balsam sections of a cornea which has been stained 

 with nitrate of silver. Notice the branched cell-spaces corresponding with 

 the connective-tissue cells of the last preparation. 



[This preparation is best made by rubbing the surface of the cornea with 

 lunar caustic after scraping off the epithelium. After ten or fifteen minutes 

 (by which time the nitrate of silver will have penetrated the thickness of the 

 cornea) the eye is washed with distilled water, and exposed to the light. 

 When brown, tangential sections may be made, for which purpose the cornea 

 may be hardened in spirit.] 



LESSON XLIII. 



]. REMOVE the sclerotic from the anterior part of an eye which has been 

 preserved in Miiller's fluid, and tear off thin shreds from the surface of the 

 choroid, including amongst them portions of the ciliary muscle. Stain the 

 shreds with hsematoxylin and mount them in Farrant. Sketch the branched 

 pigment-cells, the elastic network, the mode of attachment of the fibres of 

 the ciliary muscle, etc. 



2. Injected preparation of choroid and iris. Mount in Canada balsam por- 

 tions of the choroid coat and iris from an eye, the blood-vessels of which have 

 been filled with coloured injection. Make sketches showing the arrangement 

 of the capillaries and veins. 



3. Teased preparation of retina. Break up with needles in a drop of 

 glycerine a minute fragment of retina which has been placed in 1 per cent, 

 osmic acid solution for a few hours, and has subsequently been kept in dilute 

 glycerine. Complete the separation of the retinal elements by tapping the 

 cover-glass. Draw carefully under a high power some of the isolated 

 elements e.g. the rods and cones with their attached fibres and nuclei, the 

 inner granules, the ganglion-cells, the fibres of Miiller, hexagonal pigment- 

 cells, etc. In some of the fragments the arrangement of the elements in the 

 retinal layers may be made out even better than in actual sections. 1 



Measure the length and diameter of some of the cones, the length of the 

 cone-fibres, and the diameter of some of the outer and inner nuclei. 



4. Teased preparation of lens. Separate in water the fibres of a crystalline 

 lens which has been macerated for some days in bichromate of potash solu- 

 tion. Sketch some of the fibres, together and separate. 



The eyelids (fig. 288) are covered externally by the skin, and inter- 

 nally or posteriorly by a mucous membrane, the conjunctiva, which is 

 reflected from them over the globe of the eye. They are composed in 

 the main of connective tissue, which is dense and fibrous under the 

 conjunctiva, where it forms what is known as the tarsus. 



Embedded in the tarsus is a row of long sebaceous glands (the 



1 The distribution of the nerve-fibres and cell-processes within the retina can only be 

 made out satisfactorily by the employment of Golgi's method (see Appendix). 



