THE EYE. 377 



The condition of the retinal elements at the " yellow spot' 3 

 is in many respects peculiar. In the first place, any continuous 

 layer of optic fibres is there wholly wanting, and the stratum 

 of nerve-cells, which are in close mutual apposition, lies imme- 

 diately upon the membrana limitans. Between these cells, 

 however, nerve-fibres run equally from the sides and the 

 internal end of the spot into it, either isolated or in very 

 minute bundles, and terminate in a way that cannot be accu- 

 rately determined. In the centre of the macula lutea there is 

 a thin uncoloured spot in which the granular layer is wanting, 

 from 008 — O'l'" in diameter, through which the pigment of 

 the choroid is visible — the so-termed foramen centrale. The 

 plica centralis never exists during life; but this is not the case, 

 probably, with the yellow colour, which depends upon diffused 

 pigment pervading all the parts of the retina, except the 

 "rods." The latter, in this situation, assume the form of 

 " cones" exclusively, inasmuch as the " proper rods," as Henle 

 ('Zeitsch. f. rat. Path./ 1852, II, p. 307) correctly states, are 

 wholly wanting in the " yellow spot" and its immediate neigh- 

 bourhood. Instead of them, the "cones" form a perfectly 

 continuous layer, are more slender than elsewhere (not more 

 than 0*002 — 00024/" in breadth), and support at their outer 

 end, here as elsewhere, not short points, as Henle states, but 

 the usual " rods," which in this situation are not more than 

 0-0006— 0-0007 /// broad (fig. 304 x ). 



After this description of the elements of the various retinal 

 layers, it will be as well to cast a glance upon their mutual 

 connexion. I have ascertained, in the human eye, that the 

 fibres proceeding from the " rods" and " cones" inwards, and 

 from the " granules," on both sides, are connected, and simply 

 constitute parts of a fibrous system of the retina, as yet not 

 recognised as a connected whole, except by H. Miiller. This 

 system, the greater number of whose elements are vertical, 

 penetrates the entire thickness of the tunic, and might be 

 termed the radiating fibre-system [radial fibres, H. Miiller), in 

 contradistinction to the horizontal, referable to the expansion 

 of the optic nerve. Proceeding from the bacillar layer, it is 

 obvious, that the fine filaments arising from the "rods" and 

 " cones" are directly continuous with the similar processes 

 given off from the external side of the " granules," in such a 



