. Comparative anatomy. Anatomy, Comparative. 498 COMPARATIVE ANATOMY tionately. Vision in primates is more important than smell, and brain changes express relative functional values. Cortex. Two parts of the primitive vertebrate brain participate specially in the great enlargement of the cerebral hemispheres, the striate body and the neopallium. These two regions are not clearly differentiated in cyclostomes, but are distinguishable in fishes. Of the two, the pallium changes more. The hemispheres of teleost fishes have a thin epithelial pallium or mantle. Compared with the mantle' of teleosts,
. Comparative anatomy. Anatomy, Comparative. 498 COMPARATIVE ANATOMY tionately. Vision in primates is more important than smell, and brain changes express relative functional values. Cortex. Two parts of the primitive vertebrate brain participate specially in the great enlargement of the cerebral hemispheres, the striate body and the neopallium. These two regions are not clearly differentiated in cyclostomes, but are distinguishable in fishes. Of the two, the pallium changes more. The hemispheres of teleost fishes have a thin epithelial pallium or mantle. Compared with the mantle' of teleosts, that of elasmobranchs and dipnoi, which are more directly in the line of mam-. B C ' ' D Fig. 413.—Horizontal diagrams of ichthyopsid brains. A, sturgeon; B, elasmo- branch; C, teleost; D, amphibian. Primitive forebrain wall stippled; telencephalic evaginations horizontally lined; thalamus vertical lines, c, common ventricle, /, interventricular foramen; I, lateral ventricle; m, midbrain; o, olfactory bulb; t, terminal lamina; II, optic nerve; 3, third ventricle. (From Kingsley's "Comparative Anatomy of Vertebrates," after Herrick.) malian ancestry, is relatively thick. Homologies with the pallium of higher vertebrates are difficult on account of the lack of differentiation. In the pallium of fishes the cellular gray matter is adjacent to the ventricle, while the external layer is fibrillar. Even in the pallium of fishes, how- ever, some cells migrate from the gray into the fibrillar zone. (Fig. 413) The pallium of amphibia, taking Rana as a type, is thick, and is differentiated into a median archicortex and a lateral paleocortex, both associated with olfactory fibers. In reptiles the number of cell layers in the pallium increases to three. The medio-dorsal region of each hemisphere forms an archicortex or hippocampus. In the lateral pallium, dorsal to the striate body, are possibly the beginnings of a neocortex. A true many-layered neocortex appears in all mammals
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