742 SPECIAL HISTOLOGY. 



length of which equals half the thickness of the bacillar layer (from 

 0-007-0-015 of a line), and whose breadth is from 0-0025 to 0-0045 

 of a line. Each of these " cones" consists of an external, thicker and 

 longer, finely granular extremity, often more or less ventricose, which, 

 gradually diminishing in size, passes into a common "rod" without a 

 point, and of a shorter inner portion, somewhat constricted from the 

 other by a slight incurvation, in which an elongated or pyriform, more 

 opaque and brilliant body, 0-002-0-003 of a line in length, is enclosed. 

 On the internal aspect, these " cones," in which I can see nothing but a 

 cell with a nucleus, are, like the " rods," continued into the succeeding 

 layers of the retina, where we shall again have to consider them, by fine 

 filaments, 0-0004-0-0006 of a line in size, similar to those of the " rods." 

 The "rods" and "cones" are arranged vertically upon the retina, 

 like palisades, in close apposition, and consequently, one of their ends 

 is directed towards the choroid and the other towards the granular 

 layer. Close to the macula lutea the " cones" form an almost continu- 

 ous stratum (Fig. 304 2 ), so that the "rods" are placed only in single 

 series between them, but more anteriorly they are wider apart, the dis- 

 tance between them at first being about 0-002-0-003 of a line, and in the 

 anterior portions of the retina even 0-0004-0-005 of a line (Fig. 304 3 ), 

 thus affording room for more "rods" in the interspaces. Viewed from 

 Fi(r 3Q4 without, the bacillar layer, when its outermost sur- 



face is brought into focus, exhibits rounded spaces, 

 placed at a greater or less depth, filled with a clear 

 substance, which also occupies elsewhere the inter- 

 stices between the elements of this layer. These 

 clear spaces, corresponding to the " cones," pre- 

 sent an internal, dark, smaller circle, the terminal 

 surface or apparent transverse section of the " rod" 

 which is seated upon the "cone," and are surrounded by the closely 

 crowded terminal surfaces of the "proper rods," disposed in a sort of 

 mosaic manner, their outlines being indicated by the single, double, or 

 multiple series of reticulations (Fig. 304). 



2. The granular layer, stratum granulosum (Fig. 303 h, /), is com- 

 posed of opaque, granular corpuscles, reflecting the light tolerably 

 strongly, of a round or oval figure, and 0-002-0-004 of a line in size, 

 sometimes looking like free nuclei, sometimes like minute cells almost 

 entirely filled by large nuclei, although, according to my observations, 

 they should all be referred to the latter category. For I find, especially 

 in preparations made with chromic acid, that from both sides of every 

 granule very fine filaments, 0-0002-0-0003 of a line thick, are regularly 



Fia. 304. Bacillar layer from without. 1, at the "yellow spot" (only ' : cones"); 2, at 

 the border of the same ; 3, from the middle of the retina : a, " cones," or vacuities corre- 

 sponding with them ; 6, " rods " of the " cones," whose terminal surface is often placed rather 

 more deeply than that of the proper " rods," c. Magnified 350 diameters. 



