THE SENSES. 

 Human Eye Dissected. 



205 



C, cornea. S, sclerotic coat. X, choroid coat. R, retina. O, optic nerve. V, vitreous humor. 

 L, lens. A, aqueous humor. P, pupil. J, iris. K, ciliary processes. 



The parts of the eye remaining to be described are the humors 

 and the iris. A is the aqueous or watery humor, placed imme- 

 diately behind (C) the cornea. It is divided into an anterior and a 

 posterior chamber by (J) the iris, which floats like a curtain in it. 

 The iris is the part that gives the blue, grey, or black color to our 

 eyes, and which has in its centre an opening (P) that enlarges or 

 contracts according to the quantity of light to be admitted. It is 

 supposed to possess a circular and a radiated set of fibres to effect 

 this. Behind the aqueous humor lies the lens (L), the firmest of 

 the three humors. Its form in the human eye, as seen in the figure, 

 is something like a highly convex magnifying-glass. In fishes it 

 is globular, and it is it that falls out like a pea when the eye is boiled. 



Horizontal section of the Eye, showing the different humors. 



Behind this, again, is placed the largest or vitreous humor (V), 

 which appears of rather greater consistence than the white of an 



