370 SENSITIVE SYSTEM. 



that the existence of such a covering has been doubted ; the con- 

 tinuation, however, has obtained, oflate years, the passport of our 

 best human anatomists, which, with the corroboration of some 

 remarkable circumstances connected both with health and dis- 

 ease, appear to have set the much-agitated question at rest. 

 The conjunctiva is not thrown into wrinkles (the same as the 

 skin is) when the lids are opened : the elasticity of its cellular 

 connexions in general, particularly the one it has with the adi- 

 pose matter at the bottom of the orbit — which from being 

 stretched will recede again — being such as to prevent any cor- 

 rugation. The conjunctiva presents Iwo ample surfaces : the 

 adherent one is rough, lax in texture, and flocculent ; the inner 

 surface is smooth, glossy, and humid with secretion. In tex- 

 ture, it is no more than a finer sort of cellular membrane con- 

 densed so as to be rendered firm and resisting, in whose sub- 

 stance are distributed numerous bloodvessels, that give it a car- 

 nation hue. There are some striking varieties, however, in its 

 organization, notwithstanding it is everywhere one and the same 

 continuous membrane : e. g. the C07ijunctiva palpebralis pos- 

 sesses numerous bloodvessels, from which, as we know, it ap- 

 pears commonly red ; the conjunctiva sclerotica is comparatively 

 thick and pulpy in texture, only shewing a straggling red vessel 

 or two, and, from the nature of the part it covers, ordinarily 

 appears immaculately white ; whereas, the conjunctiva cornea, is 

 particularly thin and dense, and is transparent, and in a per- 

 fectly sound state has no appearance whatever of vascularity : 

 indeed, as was observed before, vessels were some years ago de- 

 nied to it altogether ; and their existence probably would be dis- 

 puted yet, did not inflammation of the part occasionally afford 

 us ocular demonstration of them. 



Organization of the Eyelids. — The eyelids receive their vessels 

 from the orbito-frontal, facial, and temporal arteries. Their veins 

 terminate in the corresponding venous trunks. They derive their 

 nerves from the fifth pair, and are very sensitive and irritable 

 parts. 



Use of the Eyelids. — Comparing the eye to a window, the lids 

 may be regarded as the shutters ; their uses being to exclude 

 light and to protect the organ from all violence or accident. 

 Light being its natural excitant, exclusion puts the organ into a 

 state of repose, and enables it to recruit those energies which 

 intense or long-continued vision may have weakened or ex- 

 hausted. During sleep, the hds are closed for this purpose : not, 

 however, that this is absolutely necessary ; for let the nervous ex- 

 citability be withheld or suspended, and the organ will be equally 

 in a state of repose, as is the case with those individuals who 



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