The elasmobranch fishes . elasmobranchfish03dani Year: 1934 IX NERVOUS SYSTEM NERVOUS SYSTEM OF HEPTANCHUS MACULATUS Central Nervous System BRAIN The brain of Heptanchus maculatiis may be described as made up of five divisions, as is common for the Elasmobranchs. These divisions, beginning anteriorly are: the telencephalon, the diencephalon. the mesencephalon, the metencephalon, and the mj^elencephalon. The telencephalon (//., fig. 200a ), if seen from the dorsal side, appears as a bilobed mass which is continued forward by long olfactory tracts (). Between the tracts and projecting slig
The elasmobranch fishes . elasmobranchfish03dani Year: 1934 IX NERVOUS SYSTEM NERVOUS SYSTEM OF HEPTANCHUS MACULATUS Central Nervous System BRAIN The brain of Heptanchus maculatiis may be described as made up of five divisions, as is common for the Elasmobranchs. These divisions, beginning anteriorly are: the telencephalon, the diencephalon. the mesencephalon, the metencephalon, and the mj^elencephalon. The telencephalon (//., fig. 200a ), if seen from the dorsal side, appears as a bilobed mass which is continued forward by long olfactory tracts (). Between the tracts and projecting slightly anteriorly is the median olfactory nucleus (), better seen in ventral view (fig. 200b). Dorsally the telencephalon is raised up into the so- called pallial eminences. At the angle be- tween the median olfactory nucleus and the pallial eminence is the recessus neuro- porieus, at the sides of which arises the terminal nerve (tn.). The telencephalon is continued posteriorly by the diencepha- lon (fZf, fig. 200b). The diencephalon is provided with a thin roof through which the pineal stalk passes as a slender thread upward and forward to the cartilaginous roof. This segment of the brain continues posteriorly as a gradually narrowing mass back to the place where the optic nerves (//) form the optic chiasma. From the posterior and ventral part of this division arises the in- fundibulum, at the sides of which are the inferior lobes () and the vascular sacs () of the brain. In the middle line and ventral to the vascular sacs are the lobes of the pituitary (see fig. 215). The mesencephalon is well developed (ins., fig. 200b) . Dorsally it consists of two hollow optic lobes (, fig. 200a) or corpora bigemina. These in their posterior part are overlapped by the cerebellum (cb.) and ventrally by the infundibnlum and its associated structures. Through the posterior roof of md. V. Fig. 200b. Brain and cranial nerves, Heptanchus maculafus, ventral view. For explanation
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