XI EYE 183 



The interior of the globe ( F. H) is filled with a colour- 

 less, transparent jelly, the vitreous humour, surrounding 

 which, everywhere but on its external face, is a thin semi- 

 transparent membrane, reddish when perfectly fresh, but 

 becoming grey soon after death ; this is the retina {R). 

 Between the retina and the sclerotic is a membrane called 

 the choroid {Ch), the inner face of which, i.e., that in contact 

 with the retina, is coloured black. It is this layer of black 

 pigment which gives the dark tint to the semi-transparent 

 sclerotic in the entire eye ; strictly speaking, it is the inner- 

 most layer of the retina, but actually it adheres to the 

 choroid and appears like the innermost layer of that coat. 

 The retina is readily detachable from the choroid, but at 

 the place where the optic nerve enters {blind spot) it be- 

 comes continuous with the fibres of the latter, which pass 

 through the sclerotic and choroid. The choroid is made 

 up of connective tissue and contains numerous blood- 

 vessels as well as pigment-cells. 



Lying just internal to the pupil is a nearly globular body, 

 perfectly transparent when fresh, the crystalline lens (Z) ; it 

 is kept in place by a delicate membrane, the capsule of the 

 lens. The iris, which covers the outer face of the lens 

 except where it is perforated by the pupil, is covered on its 

 inner surface with black pigment, and is continuous all 

 round its outer margin with the choroid. Between the iris 

 and the cornea is a space, the aqueous chamber of the eye, 

 which contains a watery fluid, the aqueous humour. The 

 main cavity of the eyeball, containing the vitreous humour, 

 is called the vitreous chamber ( V. H). 



The actual relations of these parts in the entire eye are 

 best grasped in a vertical section, such as is represented in 

 Fig. 57. The main part of the eyeball forms a chamber, 

 enclosed by the sclerotic, darkened internally by the choroid, 



