. On the anatomy of vertebrates. Vertebrates; Anatomy, Comparative; 1866. Section of medulla ENCEniALON OF FISHES. -273 in the ventral cohnnns a short longitndhial groove divides a .larrower median 'pre-pyramidal' tract, fig. 172, a, from a broader lateral ' olivary' tract, ib. h: in the dorsal columns a median ' funicular' tract, ib. e, is similarly marked off from a lateral ' post-pyramidal' tract, d: this is now, also, distinguished by a deeper fissure from the true lateral or ' restiform' tract, c, at the inferior part of which a distinct slender portion is also sometimes defined. The post
. On the anatomy of vertebrates. Vertebrates; Anatomy, Comparative; 1866. Section of medulla ENCEniALON OF FISHES. -273 in the ventral cohnnns a short longitndhial groove divides a .larrower median 'pre-pyramidal' tract, fig. 172, a, from a broader lateral ' olivary' tract, ib. h: in the dorsal columns a median ' funicular' tract, ib. e, is similarly marked off from a lateral ' post-pyramidal' tract, d: this is now, also, distinguished by a deeper fissure from the true lateral or ' restiform' tract, c, at the inferior part of which a distinct slender portion is also sometimes defined. The post-pyramidal tracts ' "^ diverge, expand and blend anteriorly with the similarly bulging restiform tracts, forming the sidc- â \valls of a triangular or rhoniboidal cavity, called the ' fourth ventricle,' fig. 173,7: the pre-pyramidal and olivary tracts, forming the floor of the ventricle, are covered below by a thin superficial layer of trans- verse ' arciform fibres'' ib. m, concealing their boundary fissures. At the bottom, of the ventricle "Uongata, cure/w- . rtus the myelonal canal is exposed, and its sides swell and rise as rounded or ' teretial' tracts,^ ib. /, from the floor of the ventricle, diverging slightly as they ad^â ance, and exposing an intermediate ' nodular' tract; this structure is well seen in the basking shark (Sdache) : two lateral prominent ' vagal' cokunns also project inwards into the ventricle, from the conjoined resti- form and post-pyramidal tracts; these ^"agal columns present a series of nodules, fig. 173, t, corresponding with the fasciculi of the roots of the Q;reat vagal nerve in Selache.^ In the Cyprinoid Fishes the median inferior tract rises into the ventricle, and is develoiJed into a smooth hemispheric mass, the ' nodulus,'fig. 178, k: the conjoined post-pyramidal and restiform walls swell outwards, and form lateral 'vagal' lobes, large and nodulated in the Carp, fig. 178, h, which is so tenacious of life. The vagal lobes ar
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