THE EYE. 



indistinct on treatment with acetic acid and dilute alkalies, but much more slowly 

 than connective tissue fibrils ; moreover, they are not dissolved by boiling- in water. 

 They are much less developed in the central and posterior part of the retina than in 

 the peripheral and anterior part ; towards the ora serrata they are very distinct and 

 closely set. 



Fig. 59. INTERNAL LIMITING MEMBRANE OF THE RETINA TREATED WITH SILVER NITRATE, SHOWING 



THE OUTLINES OF THE BASES OF THE MC'LLERIAN FIBRES. (RetzillS. ) 



At the lower pait of the figure some of these fibres are seen separated. 



Structure of the macula lutea and fovea centralis (fig. GO). The 

 peculiarities in structure which these present have partly been incidentally 

 noticed in the preceding description of the retinal layers. In the fovea no 

 rods are met with, and the cones, especially their inner segments, are much 

 longer and narrower than elsewhere. All the other layers are much thinned, but 

 towards the margin of the fovea they rapidly increase in thickness, and in the rest 

 of the macula lutea most of them are thicker than at any other part of the retina. 

 The ganglionic layer (fig. GO, 2) is especially thickened at the edge of the fovea, 

 the cells being from six to eight deep. They are smaller here than nearer the centre 

 of the fovea. The nerve-fibre layer (1) gradually thins and disappears as a distinct 

 layer near the edge of the fovea as the fibres join the central ends of the ganglion- 

 cells. The opposite end of each ganglion-cell is directed vertically towards the inner 

 nuclear layer. The bipolar inner granules are somewhat obliquely disposed. They 

 are smaller than the outer granules and, as elsewhere, much smaller than the ganglion- 

 cells. At the centre of the fovea they are but thinly scattered, and the inner and 

 outer molecular layers appear to join between them. At the middle of the fovea the 

 retina is very thin, consisting here mainly of the cone-cells (i.e., cones with their 

 nucleated fibres) and pigmentary layer, but a few of the inner granules are also 

 present, and one or two isolated nerve-cells (perhaps amacrine cells) may also 

 be seen very near to the centre. According to the figures and description given 

 by M. Schulbze the membrana limitans externa is also cupped in at this place, and the 

 cones, both inner and outer segments, are considerably longer than elsewhere, so that 



