. Anatomischer Anzeiger. Anatomy, Comparative; Anatomy, Comparative. 535 type we are accustomed to regard as distinctive of the Amniota. The condition of affairs represented in Lepidosiren (Fig. 17) is exactly analogous to that found in foetal mammals, more especially those (the Monotremata and Marsupialia), which have retained the dorsal part of their hippocampal arc, undisturbed by a corpus callosum. In the brains of foetal Ornithorhynchus and Perameles, which I have represented 1), the same arrangement of thalamencephalon, lamina chorioidea and mesial edge of the pallium (i. e. hippocampus)
. Anatomischer Anzeiger. Anatomy, Comparative; Anatomy, Comparative. 535 type we are accustomed to regard as distinctive of the Amniota. The condition of affairs represented in Lepidosiren (Fig. 17) is exactly analogous to that found in foetal mammals, more especially those (the Monotremata and Marsupialia), which have retained the dorsal part of their hippocampal arc, undisturbed by a corpus callosum. In the brains of foetal Ornithorhynchus and Perameles, which I have represented 1), the same arrangement of thalamencephalon, lamina chorioidea and mesial edge of the pallium (i. e. hippocampus) is found. A similar relationship will be found in the homologous parts of the brain in certain Keptiha, such, for example, as many Chelonia. But in certain other reptiles (such as Sphenodon, the Lacertilia and some of the Ophidia) there is a very striking difference in the arrangement of the nervous tissues fringing the cerebral mantle, which is, at first sight, extremely puzzling, and has given rise to great confusion in the literature relating to the comparison of the reptilian and mammalian forebrain. I have described this region of the brain in a foetal Sphen- odon (Hatteria) in considerable detail 2), and v. Kupffer ^), in his admirable account of the morphogenesis of the brain, has represented the condition of affairs in Anguis fragilis, and given an interpretation of them (p. 238), to which I shall have occasion to refer. If a coronal section be made through the cerebrum of a foetal Sphenodon or Anguis so as to pass through the foramen of Monro (Fig. 18), and this be compared with a cor- responding section in Lepidosiren (Fig. 17), it will be found that whereas, in the Dipnoi (as also in the Chelonia and Mammalia) the lamina chorioidea is attached laterally to the edge of the pallial formation, i. e. the hippocampus, in these particular reptiles a caudal prolon- gation of the paraterminal body (Fig. 18, P) is interposed between the attachment of the lamina chorioidea an
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