On the anatomy of the fovea centralis of the human retina / by J. W. Hulke.

  • Hulke, J. W.
Date:
[1867]
Catalogue details

Licence: Public Domain Mark

Credit: On the anatomy of the fovea centralis of the human retina / by J. W. Hulke. Source: Wellcome Collection.

Provider: This material has been provided by UCL Library Services. The original may be consulted at UCL (University College London)

    2/10 (page 110)
    turbed, I found the distance of the fovea from the centre of the optic nerve exactly equalled 1^'. In vertical sections through the artificially hardened macula the fovea centralis is seen to he produced by the radial di^•ergence of the cone-fibres from a central point, and by the thinning and curving of the inner retinal layers towards the outer surface of the retina as they approach this point. The thickness of the retina decreases in a rapid uniform curve from the edge to the centre of the fovea, and very slowly from the fovea! edge towards the ora retina?. Since the maximum thickness coincides with the edge, and the minimum with the centre of the fovea, the former is the most elevated, the latter the most depressed part in the macula. At the centre of the fovea, where the retina is thinnest, passing from the outer to the inner surface, we meet with the following structures:—the bacillary layer, the outer limiting membrane, a thin band of areolated connective tissue wliich transmits a few cone-hbres, the inner granule and ganglionic layers represented by scattered cells and not separated by a distinct granular layer, optic nerve-fibres, and lastly, the mner limiting membrane. Minute Structure. 1. The bacillary layer (Plate VII. fig. 1, i) in the fovea contains cones only; and rods first appear midway between the centre of the fovea and the outer border of the macula*. The foveal cones (figs. 2 & 3) are longer and more slender than those distant from the macula, and there is a similar difference in the length and stoutness of the rods. In both rods and cones an outer and an inner segment are observable; the outer in profile is a slender rectangle; the inner is flask-shaped, and is in the cones much stouter than the outer segment, while in the rods it only slightly exceeds the outer segment. The inner segment is always associated in the usual manner, by inclusion or by a communicating fibre, with an outer granule (figs. 2 & 3). Connexion by a fibre obtains (1) with the central cones whose associate outer granules are peripherally dis- placed, (2) with all cones associated with a distant outer granule, and (3) always with the rods whose smaller diameter does not allow them to include their granule. There is a definite outer limiting membrane which has the same relations to the bacillary and outer granule-layers as in other situations. Outer Grnnule-laijer (fig. 1,2).—Owing to the peripheral situation of the outer granules belonging to the central cones, this layer is absent from the centre of the fovea. It begins at a short distance from this latter, attains its maximum thickness near the foveal edge, then decreases gradually, and again increases towards the border of the macula. This variation is due to the presence, at the margin of the fovea, of the granules belonging to the central cones in addition to those connected with the cones of this part, and to * KiiLLiKEK says there arc no rods in the macula (llan(ll)iicli der Gewcbclehre, Aufl. iv. S. (5(54). This dif- fereiKX' i)i'rhaps procx-cds from the difficulty in fixing the exact extent of the macula in chromic-acid preparations, in which the colour of the spot is destroyed.