746 SPECIAL HISTOLOGY. 



together with it. Todd and Bowman describe the clear bodies above 

 noticed as cells, and also figure a minute nuclear corpuscle in them; 

 and I will not directly contradict this notion, although I have not as 

 yet been in any way able to satisfy myself of the existence of nuclei and 

 true cells in this layer. 



The condition of the retinal elements at the " yelloiv spot" 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 immediately 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 accurately 

 determined. In the centre of the macula lutea there is a thin unco- 

 lored spot in which the granular layer is wanting, from O'OS-0-1 of a line 

 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 color, 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. 807) correctly states, are wholly wanting in the 

 "yellow spot" and its immediate neighborhood. Instead of them, the 

 " cones" form a perfectly continuous layer, are more slender than else- 

 where (not more than 0-002-0*0024 of a line 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 of a line broad (Fig. 304). 



After this description of the elements of the various retinal layers, it 

 will be as well to cast a glance upon their mutual connection. 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 recognized as a connected whole, except by H. Mul- 

 ler. 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. Muller), in contradistinction to 

 the horizontal, referable to the expansion of the optic nerve. Proceed- 

 ing 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 

 way that the filaments of the " rods" (Fig. 303 *, rr) are connected. with 

 the "granules" of the outer granular layer, and those of the " cones" 

 (Fig. 303 *, r) with the " granules" of the inner layer ; in fact, each 

 "cone" or " rod" is in connection with a granule, the latter also per- 



