. On the anatomy of vertebrates. Vertebrates; Anatomy, Comparative; 1866. ENCEPHALON OF FISHES. '279 small portion of a circle, fig. 182, li; and in some bony fisli, as tlio Cxarpikc, Loach, and Lumpfish, they are scarcely raised a1)ove the level of the floor of the ventricle. They are not deve- lojied in the Polypterns, the Lei:)idosiren, or the higher Plag-iostomcs; and both tori and tnberculi are peculiar ichthyic develope- mcnts in the ventricles of the optic lobes. The bottom of the 0]rtic ventricle, fig. 184, v, anteri(3r and external to the 'tori,' is grey, and usually prominent, with w
. On the anatomy of vertebrates. Vertebrates; Anatomy, Comparative; 1866. ENCEPHALON OF FISHES. '279 small portion of a circle, fig. 182, li; and in some bony fisli, as tlio Cxarpikc, Loach, and Lumpfish, they are scarcely raised a1)ove the level of the floor of the ventricle. They are not deve- lojied in the Polypterns, the Lei:)idosiren, or the higher Plag-iostomcs; and both tori and tnberculi are peculiar ichthyic develope- mcnts in the ventricles of the optic lobes. The bottom of the 0]rtic ventricle, fig. 184, v, anteri(3r and external to the 'tori,' is grey, and usually prominent, with white fibres radiating through it to rise and expand upon the walls of the lobes. The fiptic lolies have almost coalesced in the Sturgeon, fig. Xh't, o, Poly- pterns, Lepidosiren, Amblyopsis, and Loach (Cohitis). Where they are quite distinct externally, as in most Osseous Fishes, they are brought into mutual communication by one or two commissures; the anterit^ir ' commissura transversa' is the most constant; it is shown in the Perch, fig. 182, and in tlie Plerring, fig. 184, s; it passes in front of the entry to the third ventricle. In the Myxine and Lepidosiren the prepyramidal fibres curve suddenly forward and upward before expanding into the floor and sides of the third ventricle, and they thus form a small protuberance beneath the basis of the optic lobes, fig. 186, n. In the Shark the same columns swell out laterally, and form two small protuberances, fig. 187, a, separated below by the vascular (hypophysial)" floor of the third ventricle. In most Osseous Fishes the corres- ponding fibres of the prepyrami- dal tracts swell out suddenly, be- neath the optic lobes, into two protuberant well - defined oval ganglions ('hypoaria,' fig. 185, ii, iig. 181, e) : their bulk is increased l)y added grey matter, whicli variegates their outSr surface; they are well developed in tlie common Cod, in which, as in some other fishes, they contain a cavity (hypoarian ventricle). In som
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Keywords: ., bookauthorowenrichard18041892, bookcentury1800, bookdecade1860
