284 THE RETINA, BY MAX SCHULTZE. 



the size of the external granules, or in the thickness of the 

 cone fibres between those of the area of the macula lutea in 

 question, and the more peripheric regions of the retina. On the 

 other hand, the course pursued by the cone fibres is quite dif- 

 ferent. From the date of Bergmann's observations on this point 

 it has been known that in the external granule layer, and 

 especially in the subsequent inner division of this layer, which 

 contains no cells, but free fibres alone, the course of the fibres 

 even external to the borders of the macula lutea, change from 

 a radial to a horizontal direction, which, coincidently with the 

 thickening of this layer towards the border of the fovea, becomes 

 constantly more and more oblique, so that in fact some fibres 

 even run parallel to the surface of the retina. The rod and 

 cone fibres, and afterwards the cone fibres alone, form curves 

 which, prolonged backwards, all diverge from the fovea or from 

 the visual axis, which if prolonged would pass through the fovea, 

 and thus reach the outer granulated layer ; though not by that 

 shortest path which is pursued by the more peripheric fibres 

 of the external granule layer. In consequence of the gradual 

 and necessary prolongation of the cone fibres, a layer of 

 horizontal fibres is produced, extending for some distance 

 around the fovea, the beginnings and endings of which are no 

 doubt radially directed ; but which at a certain plane stream 

 out like radii from the central fovea.* The explanation of this 

 is found in the very existence of the fovea. At this point all 

 the layers of the retina, with the exception of the cones and 

 external granules, diminish to a minimum. The cone fibres of 

 this region, in order to reach their destination, must diverge from 

 one another in all directions. Beyond the fovea are the inter- 

 nal granules belonging to them, the internal granulated or 

 molecular substance, and the ganglion cells. But from the 

 uninterrupted cone layer fresh masses of cone fibres still come 

 in order to seek their connections. And, although the ganglion- 

 cell layer becomes considerably increased in thickness at the 

 macula lutea, this is not the case with that of the internal 

 granules. The fibres thus press outwards, till ultimately 

 external to the yellow spot the direct radial course of the 



* Merkel, loc. cit, Taf. i, fig. 11. 



