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

Johnson, G. Lindsay (George Lindsay), 1853-1943.

Date:: [1900]

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)

17/142 (page 17)

$intermediate green, and the peripheral red, brown, or purple, the central zones being invariably stippled with minute dots. The distribution of the retinal vessels varies in detail, but generally three or four main branches pass diagonally from the disc to the periphery. Choroidal vessels are rarely seen ; I have only found them in the red peripheral zone of the Siamese Cat. The pupils of all the Felidse are round when fully dilated, contracting to a vertically oval slit, or in some cases even to a, straight line in all the small animals; while in all the large Felidse, viz., the Lion, Tiger, Cheetah, Puma, Ocelot, and Serval, the pupil remains round and con- tracts as with us. The smaller Felidas can absolutely exclude light by the contraction of the pupil to a vertical line (all chinks being excluded by the uveal pigment), which the larger Felidge cannot do, since round pupils cannot close entirely. Although the domestic Cat presents a general resemblance to the wild Felidas, a difference in colour of the fundus exists in every variety that I have examined, and in many cases the coloured pigment of the peripheral zone encroaches in the form of large patches on the Tapetum lucidum. Domestication and artificial selection evidently affect the colour of the Fundus oculi in a profound degree, and a study of the fundus of the numerous varieties of any of our domestic animals, more especially the Cat and Dog, would well repay the labour of investigation. I have likewise found that the refraction of domestic animals is not the same as that of the wild species—the tendency being always in the direction of myopia and astigmatism. 2. The Viverridce.—The genera Genetta and Paradoxurus closely resemble the Felidse, and in the Herpestes we have also a family likeness. The Mungoose (Her- pestes griseus) has the peculiarity of a broad prussian-blue peripheral zone, surround- ing a grass-green central area. This is the only animal in which the ophthalmoscope has revealed a prussian-blue periphery. Blue and pure purple are the rarest colours in eyes ; I have found them as narrow zones in the Racoons, Jackals, and Foxes, and occasionally distributed as patches over the fundus in the domestic Cat. The Spotted Ichneumon [Herpestes nepalensis) has the entire fundus covered with orange patches and brown dots very dense in the peripheral zone, but spread over the entire fundus. The Tayra (Galactis barbara), belonging to the Mustelidse, has similar patches over the entire fundus, whilst in the Common Otter (Lutra vulgaris) and in some of the Bears these orange patches are confined to the intermediate zone. I can offer no explanation to account for their presence. The genera Cynictis and Suricate have an appearance entirely different from that of any other of the Carnivora. The colour of the fundus is dark grey, similar to that which we have seen in some of the Primates, and such as we shall find in the Suidse. The fundus is uniform throughout ; there are no zones and no Tapetum lucidum. The cupping of the disc is absent, and there are semi-opaque nerve fibres radiating from the disc, an appearance Avhich we shall again notice in the Ungulates and Rodents. The Cynictis is the only Carnivore in which I have found a horizontally VOL. CXCIV.-- B. D$