38 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 149 



tapers forward to anterior poles nearly at the narrows of the olfactory 

 peduncles but well separated from the olfactory bulbs. The cerebral 

 hemispheres would seem comparatively smooth or lissencephalic, 

 suggesting that there were no gyri or sulci, although such, if weakly 

 developed, might have been obscured by the dura mater. There is, 

 however, a slight depression on the dorsolateral surface in the for- 

 ward portion on either side of the rubber mold, in a position of a 

 sulcus suprasylvius, although it is not a true sulcus or furrow. The 

 fissure rhinalis is clearly defined in all specimens, and it is seen that 

 the neopallium is a little less than half the depth of the endocranial 

 cast as seen in lateral view. The cerebral hemispheres are rather 

 widely separated along the midline, and the impression of the longi- 

 tudinal or sagittal sinus made on the endocranium is clearly shown. 

 Posteriorly this sinus divides, and the two branches or lateral sinuses 

 diverge obliquely across the space above the midbrain. In their 

 position relative to the midbrain one is tempted to speculate on the 

 possibility of these branches representing instead the corpora quadri- 

 gemina, but their direct continuity with the sagittal sinus makes this 

 seem highly improbable. It is interesting to note that at the con- 

 fluence of the lateral sinuses with the sagittal sinus the right branch 

 invariably leaves the union at a somewhat lower level than the left. 

 The marked size of these structures on the casts, moreover, suggests 

 the importance of these veins in Meniscotherium. In Phenacodus 

 the cast does not include the form of the sagittal and lateral venous 

 sinuses above. 



The cerebellar portion is very poorly preserved in all the casts, but 

 there is evidence that it did not rise as high as in Phenacodus. The 

 lateral surface in both natural casts, nevertheless, shows the impres- 

 sion of the petrosal. The small pedicle representing the internal 

 auditory meatus is distinct, and in one cast (A.M. 48082) its apex 

 shows the division into positions of the facial (above) and auditory 

 (below) nerves. Above this, representation of the flocculus of the 

 cerebellum shows the askew conical form, discussed above under 

 description of the petrosal, with its somewhat extended apex directed 

 posteroventrally. 



Unfortunately, none of the endocasts of Meniscotherium shows 

 much detail on the ventral surface. Both of the natural casts, how- 

 ever, show a generally rounded pyriform lobe, extending outward a 

 little beyond the neopallium, but much less inflated laterally than in 

 Phenacodus, possibly indicating a better developed sense of smell 

 in the latter. Immediately medial to the pyriform lobe is seen a very 



