itioB 



ated 



THE EYE. 



and transparent. The thickness of the cornea is everywhere the 

 same. 



The cornea covers that part of the front of the eye which is 

 coloured, and is terminated round the coloured part at the com- 

 mencement of the white of the eye. 



5. Within the cornea is a small chamber filled with a trans- 

 parent liquid, called the aqueous humour, partially divided by a 

 thin annular partition I, called the iris, in the centre of which 

 is a circular aperture P, called fas pupil. The iris is a membra- 

 neous substance varying in colour in different individuals, which 

 gives the peculiar colour to the eye. The pupil presents the 

 appearance of a black spot in the centre of the coloured part. A 

 front view of the iris and pupil is given at I and r, and a sec 



is indicated by the same letters in fig. 2. 



6. The membrane containing the aqueous humour is terminate 

 at its posterior part by a substance in the form of a double convex 

 lens, which contains another transparent liquid, called the crys- 

 talline humour. This lens K is somewhat greater in diameter than 

 the pupil, and is supported by a ring of muscles, called the ciliary 

 processes (represented at L), in such a position that its axis passes 

 through the centre of the pupil. 



Thus the crystalline and the ciliary processes, with the c 

 include the membrane containing the aqueous humour. 



7. Within the sclerotica is a second coat IS T , called the ch 

 This is a vascular membrane which lines the internal surface of 

 the sclerotic coat, and which terminates in front in the ciliary 

 processes, by which the crystalline lens is set in it in the same 

 manner as the cornea is set in the sclerotic coat. 



Some anatomists maintain that the iris is only a continuation 

 of the choroid, and that the cornea is a continuation of the 

 sclerotic coat, which there becomes transparent. The inner surface 

 of this choroid coat is covered with a slimy pigment of an intensely 

 black colour, by which the reflection of the light which enters the 

 eye is prevented. 



8. A third coat, represented at o, called the retina, from the 

 resemblance of its structure to network, lines this black coating, 



The internal chamber Q of the eye-ball is filled with a trans- 

 parent liquor, called the vitreous humour, which is included in 

 a membraneous capsule, called the hyaloid. 



Thus between the cornea and the posterior surface of the eye 

 there are three successive humours ; the aqueous, contained by 

 the cornea ; the crystalline, contained by the crystalline lens ; 

 and the vitreous, which fills the inner and larger chamber of the 

 eve -ball. 



9. A straight line ir T passing through the centre of the cornea, 



