SENSITIVE SYSTEM. 369 



serves to prevent the gumming or agglutination of the lids to- 

 gether by the mucilaginous matter contained in the tears. 



Cellular Tissue. — The several textures we have been examin- 

 ing, including the liuiiig membrane (yet to be described), are all 

 connected together by a fine cellular tissue, destitute of fat ; 

 adipose substance here would not only have proved burdensome 

 and inconvenient to motion, but by accumulation must ine- 

 vitably have permanently closed up the eyelids ; an efiect that 

 does occasionally happen from serous effusion, to which they are 

 from their loose contexture particularly liable. 



Tunica Conjunctiva. 



The tunica conjunctiva is the membrane lining the lids, and 

 from them reflected upon the eyeball — hence the derivation of 

 the epithet conjunctiva : it has been styled also f he tunica adnata, 

 from a notion that it arises from, or grows to, the globe of the 

 eye. To convey a familiar notion of its extent and reflections, 

 it may be remarked, that if I introduce a probe or my finger be- 

 tween the lid and the eyeball, and attempt to push it to the back 

 of the orbit, I find that I am suddenly arrested, and that I can- 

 not effect my purpose, try what point 1 may, in consequence of 

 meeting with a duplicature of conjunctiva: nay, more, 1 find I 

 am unable even to touch any part but what is covered by this 

 membrane. For, after it has given an entire lining to both the 

 lids, even to their edges, where it is pierced by the ducts of the 

 Meibomian glands, and after it has given coverings to the mem- 

 brana nictitans, caruncula lachrymalis, and puncta lachrymalia, 

 it leaves the lids and becomes reflected upon the globe, to the 

 anterior hemisphere of which it likewise gives a complete cover- 

 ing ; so that it is the angle of reflection of this membrane that 

 forms the boundary between the closed and open cavities of the 

 orbit — between the tangible and intangible parts of the globe, 

 and that which prevents the probe or finger from reaching the 

 bottom of the eye. Being the common investing and connecting- 

 substance of such moveable parts as these, we find the mem- 

 brane running into loose folds in passing from one part to ano- 

 ther, and these folds furnished with abundance of cellular tissue. 

 In tracing its connexions, we may begin along the line of the 

 cilia, where it forms a union with the common skin ; in passing- 

 backward it adheres closely to the tarsi, and afterwards has a 

 loose connexion with the tarsal ligaments; it gives the membrana 

 nictitans a close tense covering, but is thrown into folds around 

 its base ; lastly, it adheres but loosely to the opaque cornea, but 

 is intimately and inseparably united with the transparent part: 

 indeed, so perfectly is the membrane incorporated with the latter, 

 8 B 



