212 THE ESSENTIALS OF HISTOLOGY 



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, placed in spirit, and exposed 

 to the light. When brown and sufficiently hardened, tangential sections may 

 be made with a razor.] 



LESSON XL. 



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

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

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

 shreds with logwood and mount them in Farrant's solution. Sketch the 

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

 fibres of the ciliary muscle, &c. 



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 Muller, hexagonal pigment- 

 cells, &c. In some of the fragments the arrangement of the elements in the 

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



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 weak bichromate of potash 

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



The eyelids (fig. 247) are covered externally by the skin, and in- 

 ternally 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 Mei- 

 bomian glands, /), the ducts of which open at the edge of the eyelid. 

 The rest of the thickness of the eyelid is composed of a somewhat 

 loose connective tissue, and contains the bundles of the orbicularis 

 muscle (b). In the upper eyelid the levator palpebrce is inserted into 

 the tarsus by a fibrous expansion, and some bundles of involuntary 

 muscle are also present near the attachment of the eyelid. The skin 



