202 



PHYSIOLOGY. 

 Fig. 6. 



Section of the eye magnified, showing the Crystalline Lens in its 

 proper situation, between the aqueous and vitreous humours. 



21. The Vitreous Humour. -The vitreous body or humour 

 is so called from its resemblance to melted glass. It is, like 

 the other humours, perfectly transparent, and occupies the 

 globe of the eye, of which it constitutes at least the poste- 

 rior two thirds. It is surrounded by the retina in nearly its 

 whole extent, to which, however, it does not adhere. It is 

 composed of a fluid, contained in cells, formed of a mem- 

 brane called the hyaloid, which communicate with each 

 other, so that if it is punctured, the fluid with ^hich it is 

 filled will escape, though slowly in consequence of the intri- 

 cacy of the cellular structure. On removing the vitreous 

 humour from the eye, it appears to be of about the consis- 

 tency of the white of an egg ; its use being to afford a sur- 

 face for the extension of the expanded retina, to keep the 

 lens at the requisite distance, and to transmit and refract the 

 rays of light. 



