Contributions to the comparative anatomy of the mammalian eye : chiefly based on ophthalmic examination / by George Lindsay Johnson.

  • George Lindsay Johnson
Date:
[1900]
Catalogue details

Licence: In copyright

Credit: Contributions to the comparative anatomy of the mammalian eye : chiefly based on ophthalmic examination / by George Lindsay Johnson. Source: Wellcome Collection.

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

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    colour is pink, and covered with a coarse pigment network as in Cynictik The disc of the Reindeer (Rangifer tarandus) follows much the same plan, but the pigment network is less marked. Opaque nerve fibres radiate brush-like from the ends and top of the disc. The Dorcas Gazelle (Gazetta dorcas) has a long oval simple disc covered with pigment network, but the opaque nerve fibres are less marked. The retinal vessels arise from three sources as in the Hog Deer, the two lateral trunks spread irregularly over the pigment zone below the disc, while the great main arterial trunk ascends vertically through the green zone, and is distributed in the characteristic way. In all the Cervidae examined I have noticed a white fibrous band, extending from the central trunk at its entrance in the disc to the posterior capsule of the lens (fig. 1, a and b, Plate 28). This phylogenetically important organ will be discussed in the chapter dealing with vestigial relics and congenital defects (see p. 53). 3. Cameliche.—An examination of several species of the Dromedary (Camelus dromedarius), the Bactrian Camel (Camelus bactricmus), and the Llama [Llama peruviana) showed no essential individual differences, the Dromedary being practi- cally indentical with the Camel. None of the Camelidse have any peripheral zone, the fundus being of a uniform colour. These are also the only Ungulates in which any choroidal vessels can be seen—a feature peculiar to red or brownish-red fundi. The Camel has a brownish-red fundus slightly stippled with dark grey dots everywhere. The disc is round, depressed below the surrounding level, and the arteries and veins, which are both of a bright scarlet, are arranged in the way we noticed in all the other Ruminants. Opaque nerve fibres radiate horizontally and downwards from the disc, while a broad zone, free from blood-vessels, with opaque nerve fibres and stippling, extends as a horizontal streak immediately above the disc. The Llama has a very large slightly oval disc, but the distribution of vessels is the same as in the Camel. The fundus is of a brilliant magenta, covered with deep red choroidal vessels and stippled everywhere below the disc with dark red dots. There are no opaque nerve fibres, but the special sensitive area immediately above the disc forms a horizontal band nearly devoid of blood vessels, as in the Camel. As already observed, the Camelidse have no Tapetum lucidum. 4. Tragulidce. Chevrotain (Tragulus javanicus).—The disc and the distribution or the vessels in this animal closely resemble those of the Cervidse, except that the disc is still more densely pigmented and perfectly oval, and the vessels all arise from the centre of the disc. The fundus above the disc is a pale yellow-green, dotted every- where at regular intervals with large stellate brown dots. The peripheral zone con- sists of an agglomeration of violet-brown pigment spots, giving it a mossy appearance. There are no opaque nerve fibres, but there is a well-marked, bloodless, sensitive area. The Chevrotain possesses a peculiarity otherwise met with in the Leporidae only, viz., that the retinal vessels stand out above the surface of the retina in such a manner as to cast broad shadows on to the brilliant green background. To focus
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