Chap. 41.] Humours of the Eye. , 



The vitreous humour was fo called from a fuppofed 

 refemblance to melted glafs ; It is a clear and gelatinous 

 fluid, very much refembling the white of an egg It 

 fills about three fourths of the globe of the eye, ancj 

 extends from the pofterior part of the eye as far as the 

 ciliary ligament. It is contained in a fine tranfparent 

 capfule or membrajie, and being dexteroufly removed 

 from the globe of the eye, prelerves its confidence for 

 ibine time, being fupported by its capfule, but after- 

 wards runs off, and the capfule ilirinks by degrees. 

 The thin capfule which furrounds the vitreous humour 

 fends off a number of membraneous procefies into the 

 vitreous fubftance, where they form cells, which com- 

 municate with each other, and afford a greater degree 

 of firmnefs and tenacity to the whole mais. 



The anterior part of the vitreous humour is exca- 

 vated for the reception of the crydalline. This body 

 has the confidence of very firm jelly, and has the form 

 of a lens more convex behind than before. It is moft 

 properly denominated the cryftalline lens, and is in- 

 veiled with a capfule, which is derived from that of the 

 vitreous humour, or at lead connected with it. Steno 

 pbferved, that the lens was compofed of concentric 

 lamellas, and Zinn has difcovered radiated ftreaks of a 

 pearl colour, dividing it into little triangles. The 

 colour and confidence of the cryftalline humour varies 

 at different ages. Till the age of thirty it is very tranf- 

 parent, and alrnoft without any colour. It after wards 

 becomes yellowiih, and that yeilownefs gradually in- 

 creafes. Till the age of twenty the confidence of the 

 Jens is generally uniform throughout ; from this time 

 it becomes hardeft in the middle, and tju's hardnefs 

 gradually increafes, and extends towards the furface *. 



The 



* The cryftalline lens in fifh is completely fpherical, and is 



fnorc denfe than, in terreftrial animals. This difference is to be 



C c 3 accounted 



