. On the anatomy of vertebrates. Vertebrates; Anatomy, Comparative; 1866. 278 ANATOMY OF the Chimasra, fig. 179, o, and in the Sharks, fig. 187, O. In the latter they bear the same proportion to the optic nerves and eyes as in other fishes, their small relative size depending on the advanced developement of both cerebellura and cere- brum : in the blind Amblyojjs of the svibterraneous waters, the diminution of the optic lobes relates to the almost total abrogation of the visual organ; but since both in the Amblyops and the equally blind Myxine these lobes are present, they cannot
. On the anatomy of vertebrates. Vertebrates; Anatomy, Comparative; 1866. 278 ANATOMY OF the Chimasra, fig. 179, o, and in the Sharks, fig. 187, O. In the latter they bear the same proportion to the optic nerves and eyes as in other fishes, their small relative size depending on the advanced developement of both cerebellura and cere- brum : in the blind Amblyojjs of the svibterraneous waters, the diminution of the optic lobes relates to the almost total abrogation of the visual organ; but since both in the Amblyops and the equally blind Myxine these lobes are present, they cannot be exclusively the central ganglion of the optic nerve, nor their sole function that of receiving the impressions of the sense of sight, and making them jjerceptible as ideas by the animal. The optic lobes are hollow in most Fishes, fig. 182, b. The exterior surface shows Ijlended grey and white matter, the white 182 fibres usually converging to the optic nerves; some of the fibres unite with the anterior crura of the cerebellum to form the septum of the optic lobes, fig. 184:, r, which consists of two or four medvdlary fasciculi, decreasing in the Tench, increasing in the Cod, as they pass forward. On divaricating the optic above, as in fig. 182, or by a horizontal section, as in fig. 183, their cavity, d, or ventricle, is exposetl: it communicates with the expanded myelen- cephalous canal, called ' third ' and ' fourth ' ventricles, as shown by the bristle, q. Its floor is variously configurated in dift'erent fishes. There are one or two small white tubercles, ' tiiberculi optici,' figs. 182,183, c, on each side of the back part of the septum; the Cod, Salmon, Pike, and Perch, show four of these bodies; the Carp and Herring, fig. 18-1, t, two: in the Carp they are oblong, juxtaposed, and were called 'tuberculura cordiforme' by Haller;' they are not present in the Polypterus, Lepidosiren, Sturgeon, or Plao'iostome fishes. External to these tubercles the floor of th
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Keywords: ., bookauthorowenrichard18041892, bookcentury1800, bookdecade1860
