. Compendium of histology. Histology. THE EYE. 255. The rods acquire their greatest length, mm. and more, at the bottom of the retina. Further forwards they become shorter, towards the ora serrata they are only mm. high. Their diameter may be estimated at to mm. Downwards or inwards, beneath the membrana limitans externa, the rod becomes pointed, and runs out into an ex- traordinarily fine filament, a primitive nerve fibrilla (Fig. 203, B, Fig. 204, 1, 4, Fig. 205, 1,.3). The latter passes through the outer granular layer verti- cally (and also radially). A small cell
. Compendium of histology. Histology. THE EYE. 255. The rods acquire their greatest length, mm. and more, at the bottom of the retina. Further forwards they become shorter, towards the ora serrata they are only mm. high. Their diameter may be estimated at to mm. Downwards or inwards, beneath the membrana limitans externa, the rod becomes pointed, and runs out into an ex- traordinarily fine filament, a primitive nerve fibrilla (Fig. 203, B, Fig. 204, 1, 4, Fig. 205, 1,.3). The latter passes through the outer granular layer verti- cally (and also radially). A small cell, the so-called " rod granule" (Fig. 203, B, b\ Fig. 204, 1, 2, 3, Fig. 205, 3) is embedded in its course, sometimes higher up, sometimes further down- wards. This granule forms the single element of the outer granular layer. Still more complicated textural con- ditions have been observed in the rods (Fig. 204). At the border of the in- ner member towards the outer mem- ber, embedded in the former, a plano- convex body has been found with its plane base directed upwards (1, a, 2). " rod-ellipsoid " of Krause. Furthermore, as has been long known, the outer member breaks up into transverse plates (3). These discs may have a thickness of to mm. in man (Schultze). The outer member shows a longitudinal striation, caused by longitudinal, channel-like depressions, with longitudinal elevations springing up between them, like a fluted column (Fig. 204, i, 2, and Fig. 205, I a). Longitudinal striations have also been subsequently discovered on the inner members (Fig. 205, 1, and 3 b). In the axis of the rod a very fine filament, a primitive nerve fibrilla, is also said to have been noticed (Ritter). Fig. 204.—Final structure of the rods ; I, from the chicken with the outer and inner mem- ber, as well as the cone-ellip- soid ; 2, from the frog ; 3, the outer member of the rod of a frog dividing into transverse discs; 4. rod with granule from the Guinea-
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