THE EYE AND VISION. 



[CH. LV. 



lymph spaces filled with fluid, called the spaces of Fontana. 

 They are little developed in the human cornea. 



The spaces which are present in the broken up bundles of 

 corneal tissue at the angle of the iris, are continuous with the 

 larger lymphatic space of the anterior chamber. Above the angle 

 at the corneo-scleral junction is a canal, which is called the canal 

 of Schlemm. It is a lymphatic channel. 



Structure of the Retina. The retina (fig. 569) is a delicate 



membrane, concave with 

 the concavity directed 

 forwards and apparently 

 ending in front, near the 

 outer part of the ciliary 

 processes, in a finely- 

 notched edge, the ora 

 serrata, but really repre- 

 sented by the uvea to the 

 very margin of the pupil. 

 It results from the expan- 

 sion of the optic nerve, of 

 whose terminal fibres, de- 

 prived of their external 

 white substance, together 

 with nerve-cells, it is es- 

 sentially composed. The 

 presence of nerve-cells in 

 the retina which come 

 into contact with the rods 

 and cones (visual nerve- 

 epithelium) reminds us 

 that the optic, like the 

 olfactory nerve, is not a 

 mere nerve, but an out- 

 growth of the brain. 



In the centre of the 

 retina is a round yellowish 

 elevated spot, about -+ 

 of an inch (i mm.) in 

 diameter, having a depres- 

 sion in the centre, called 



Fig. 569. A section of the retina, choroid, and part 

 of the sclerotic, moderately magnified ; a, mem- 

 brana limitans interna ; b, nerve-fibre layer 

 traversed by Mailer's sustentacular fibres ; 

 c, ganglion-cell layer; d, internal molecular 

 layer ; e, internal nuclear layer ; /, external 

 molecular layer ; g, external nuclear layer ; 

 h, membrana limitans externa, running along 

 the lower part of i, the layer of rods and cones ; 

 k, pigment cell layer ; /, m, internal and external 

 vascular portions of the choroid, the first 

 containing capillaries, the second larger blood- 

 vessels, cut in transverse section ; n, sclerotic. 

 (W. Pye.) 



after its discoverer the 



macula lutea, or yellow spot of Scemmering. The depression in 

 its centre is called the fovea centralis. About -^ of an inch 

 (2-5 mm.) to the inner side of the yellow spot, is the point 



