STRUCTURE OF THE EYELIDS. 257 



LESSONS XLIL AND XLIIL 



STRUCTURE OF THE EYELIDS AND OF THE PARTS OF 

 THE EYEBALL. 



LESSON XLII. 



1. SECTIONS of the eyelid vertical to its surfaces and transverse to its long 

 axis. The lid should be hardened in alcohol, and the sections may be stained 

 with haematoxylin and mounted in the usual manner in Canada balsam. 



Notice the long sacculated Meibomian glands lying in dense connective 

 tissue close to the conjunctival surface, and their ducts opening at the 

 margin of the lid. External to these the small fibres of the orbicularis pal- 

 pebrarum cut across ; a few of the fibres of the muscle lie on the conjunctival 

 side of the duct. A short distance from the Meibomian gland may be 

 observed another tolerably large sebaceous gland ; outside this again are the 

 eyelashes. In the skin covering the outer surface of the eyelid a few small 

 hairs may be seen. At the attached part of the eyelid are some bundles of 

 involuntary muscular fibres cut longitudinally in the section, and in the upper 

 eyelid the fibrous attachment of the elevator muscle may be observed attached 

 to the dense connective tissue. 



Make a general sketch under a low power. 



2. Sections through the posterior part of an eyeball that has been hardened 

 in Mliller's fluid. The sections are stained and mounted in the usual way. 

 These sections will show the relative thickness of the several coats and the 

 layers of which each coat is formed. Sections which pass through the point 

 of entrance of the optic nerve will also exhibit the manner in which the 

 nerve-fibres pierce the several coats to reach the inner surface of the retina. 

 The modifications which are found in the neighbourhood of the yellow spot 

 may also be made out if the sections have been taken from the human eye. 



3. Sections of the anterior half of an eyeball which has been hardened in 

 Miiller's fluid. These sections should pass through the middle of the cornea. 

 The lens may be left in situ, but this renders the preparation of the sections 

 and the mounting of them much more difficult on account of the extreme 

 hardness which is imparted to the lens-tissue by alcohol. 1 



In these sections make a general sketch under a low power, showing the 

 relations of the several parts one with another ; and study carefully, and sketch 

 in detail, the layers of the cornea, the place of junction of the cornea and 

 sclerotic, the ciliary muscle, the muscular tissue of the iris, the mode of sus- 

 pension of the lens, and the pars ciliaris retinae. 



4. Mount in glycerine thin tangential sections of a cornea stained with 

 chloride of gold by Cohnheim's method. Sketch three or four of the con- 

 nective-tissue cells (corneal corpuscles). The arrangement and distribution 



1 The celloidin method of embedding is well-adapted for preparations of this kind (see 

 Appendix). 



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