. Bulletin of the British Museum (Natural History), Geology. 496 MEGISTOTHERIUM FROM Brain. The endocast taken from specimen M26515 shows that the brain was basically similar to that of Hyaenodon and Pterodon, though larger and rather more complex. The olfactory lobes and the anterior of the cerebrum are lacking and the volume of the remaining brain is around 280 cc; thus the total brain volume cannot have been less than 300 cc but may have been over 400 cc. The cerebrum has a well developed series of sulci, four from the median Une to the pyriform lobe. The sulci are traversed by a series of
. Bulletin of the British Museum (Natural History), Geology. 496 MEGISTOTHERIUM FROM Brain. The endocast taken from specimen M26515 shows that the brain was basically similar to that of Hyaenodon and Pterodon, though larger and rather more complex. The olfactory lobes and the anterior of the cerebrum are lacking and the volume of the remaining brain is around 280 cc; thus the total brain volume cannot have been less than 300 cc but may have been over 400 cc. The cerebrum has a well developed series of sulci, four from the median Une to the pyriform lobe. The sulci are traversed by a series of blood vessels which give the whole a chequerboard appearance. Unlike Pterodon, the pyriform lobe is well developed. The tentorium separating the cerebrum from the cerebellum is inclined to the brain axis at 50°; this steep angle allows for a larger cerebrum and it completely masks the mid brain and no trace of the quadrigeminae are visible, a feature which is markedly different from Hyaenodon and Pterodon in which the quadrigeminal tubercles are exposed. The cerebellum is large, occupying perhaps as much as 25% of the brain volume; it is clearly divided into vermis and two lateral lobes, and their surface is corrugated. On the ventral surface the beginnings of the olfactory tracts can be seen anterior to the optic chiasma. The hypophysis has no definable lateral extent and appears to merge with the optic tracts, between which can be seen the loop made by the oculomotor nerve. Lateral to this the trigeminal and facial nerves issue. There is no distinct pons varolii and in this region the medulla oblongata is obscured only by the passage of the pyramidal c m. Fig. 9. Megistotherinm osteothlastes gen. et sp. nov. Brain endocast. Dorsal aspect. From cranium (M26515), Gebel 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 r
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