. Amphioxus and the ancestry of the vertebrates. Amphioxus; Sea squirts; Hemichordata. 284 THE PROTOCHORDATA. evagination from the floor of the brain, occurring behind the anterior terminal extremity of the brain. It follows that the morphological anterior extremity of the craniate brain coincides with the median lobiis olfac- torius impar, which also represents the point of last con- nexion of the medullary tube with the superjacent ecto- derm. The lobus olfactorius impar lies in the anterior vertical wall, which forms the boundary of the primary fore-brain in front, known as the lamina termi
. Amphioxus and the ancestry of the vertebrates. Amphioxus; Sea squirts; Hemichordata. 284 THE PROTOCHORDATA. evagination from the floor of the brain, occurring behind the anterior terminal extremity of the brain. It follows that the morphological anterior extremity of the craniate brain coincides with the median lobiis olfac- torius impar, which also represents the point of last con- nexion of the medullary tube with the superjacent ecto- derm. The lobus olfactorius impar lies in the anterior vertical wall, which forms the boundary of the primary fore-brain in front, known as the lamina terminahs. Rabl- RtJCKHARD has also observed the median olfactory lobe in. 0:C -irif Fig. 134. — Sagittal section through the head of an embryo of Acanthias. (After Rabl-Ruckhard.) ax. Position of anterior commissure, al. Alimentary canal, cer. Cerebellum. ch, Notochord; the black shading below the notochord indicates the aorta. /*. Fore-brain, Hind-brain, hy. Hypophysis, already shut off from the stomodoeum and lying as a closed sac at the base of inf, the infundibulum. 1,0. Lobus olfactorius. m. Mouth, Mid-brain, Optic chiasma. Pineal body (epiphysis). the Selachian embryo (Fig. 134), and it has since been found by Burckhardt in other forms. It can thus hardly be doubted that the median rudi- mentary olfactory lobe of the embryos of the higher Vertebrates is homologous with the lobus olfactorius of Amphioxus (Fig. 51), and, like the latter, represents the remains of the neuropore. In Amphioxus, however, the. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Willey, Arthur, 1867-. New York, London, Macmillan
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