. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology. Morphology and Relationships of Holocephali • Stahl 163 Nicol, 1950). From the evidence presented in these papers, it seems that the holo- cephahan ner\ous system retains some char- acteristics that must surely he primitive hut exhihits pecuHarities which are generally interpreted as secondary phenomena. Although the form of the spinal cord is quite regularly shark-like, the hrain is of an extraordinary nature. In its posterior por- tion it resemhles closely the selachian organ, but the telencephalon is unique in the
. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology. Morphology and Relationships of Holocephali • Stahl 163 Nicol, 1950). From the evidence presented in these papers, it seems that the holo- cephahan ner\ous system retains some char- acteristics that must surely he primitive hut exhihits pecuHarities which are generally interpreted as secondary phenomena. Although the form of the spinal cord is quite regularly shark-like, the hrain is of an extraordinary nature. In its posterior por- tion it resemhles closely the selachian organ, but the telencephalon is unique in the ani- mal kingdom. In Chimacm and CoUorliyn- chus\ this anterior region of the brain extends forward as a long stalk beneath the interorbital septum. It widens finally into a subdivided telencephalic lobe just behind the olfactory bulbs associated with the nos- trils. The uniqueness of the arrangement argues for its secondary development. Kap- pers and Carpentier (1911) have considered the elongation of the telencephalon and feel that it has taken place as a corollary to the enlargement of the eyes. Since the eyes have encroached upon the medial region normally occupied by the cerebral hemispheres, the forepart of the brain has been displaced. Rather than being com- pressed posteriorly, in the ancestors of the Holocephali, alone among all the animals that have developed enormous eyes, the telencephalon became displaced anteriorly. The result of the forsvard gro\\'th of the telencephalon has been the creation of long brain stalks through which regular connec- tions with the diencephalon are maintained. RJiinochimaera, in which the eyes are smaller, the brainstalks not quite so elon- gated, and the olfactory tracts more sela- chian-like, may represent an earlier stage in the evolution of this curious arrangement. Another characteristic of the telencepha- lon which lends itself to comment of a phylogenetic nature is the development of the pallium. Holmgren, who has studied forebr
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