. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology. D. Fig. 2. Transverse section of the forebrain in A, Acanthias, B, Chimaera, C, Protopferus, D, Lepidosfeus, to show position of the palhum. epnd., Ependyma; , general pallial cortex; , hippocampal lobe; , lateral limit of pallium; , nucleus olfactorius lateralis; pal., pollium; , pyriform cortex; , subpallium. (After Holmgren.) the dorsal gap. The palHum is evaginated to form two separate olfactory lobes which carry separate ventricles forward of the foramen of Munro. The pallium is r
. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology. D. Fig. 2. Transverse section of the forebrain in A, Acanthias, B, Chimaera, C, Protopferus, D, Lepidosfeus, to show position of the palhum. epnd., Ependyma; , general pallial cortex; , hippocampal lobe; , lateral limit of pallium; , nucleus olfactorius lateralis; pal., pollium; , pyriform cortex; , subpallium. (After Holmgren.) the dorsal gap. The palHum is evaginated to form two separate olfactory lobes which carry separate ventricles forward of the foramen of Munro. The pallium is rather small, being confined to the anterior, en- larged portion of the telencephalon. The brainstalks which connect the anterior en- largement with the remainder of the brain are composed entirely of subpallial tissue. Kappers, who reviewed holocephalian brain structure in his compendium on the nervous system of vertebrates (1936), grouped the Holocephali with the lower actinopterygian fishes as intermediate be- tween selachians and teleosts. He regarded the inversion of the pallium as carried over from the former and the eversion of the brainstalk walls as presaging the great pal- lial eversion of the latter. Holmgren dis- agrees with the conclusion of Kappers, however. He feels that eversion of the sub- pallial tissue of which the brainstalks con- sist cannot be regarded as an early stage of the pallial eversion seen in bony fish. In making his interpretation of the phylo- genetic position of the Holocephali, Holm- gren considers only the true pallium whose limits he has determined by histological study. He reasons that the holocephalian pallium resembles most nearly, in its degree of inversion and evagination, what must have been the type ancestral to that of ex- tant cartilaginous and bony fishes. The development of greater inversion with re- sulting fusion across the dorsal midline would lead to the selachian condition, whereas the development of thicker and more widely se
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