350 ROY L. MOODIE 
of these two otherwise closely comparable brains. Judging from 
the portion of an olfactory bulb remaining on one of the endo- 
cranial casts (figs. 7 and 8), the Oligocene hedgehogs were fos- 
sorial, since to this underground habit is ascribed the huge 
olfactory development in the recent form. The olfactory tubercle 
is not so prominent in the ancient as in the modern form, though 
its position is well shown in figure 6, where the olfactory trigone 
may also be discerned. ‘The rhinal fissure on the ancient form 
is much lower in position, and this rather strikingly increases the 
neopallial surface in the ancient brain which is so greatly reduced 
in the modernform. A slight anterior depression, not so strongly 
marked as in the modern hedgehog, marks the impression known 
as the sulcus orbitalis. The pyriform lobe in the ancient form 
is less developed, but its condition is well shown in figure 8. 
The basis cerebri is well displayed in one specimen, no. 2762, 
and reveals some things of importance. The optic chiasma is 
placed well anteriorly, being only 4 mm. posterior to the base 
of the olfactory bulb. The olfactory trigone and tubercle are 
both evident as smooth but not very prominent areas. The 
bases of the trigeminal nerves are quite large and placed well 
together. Posterior to these arise the cerebral peduncles which 
are evident as narrow indistinct bands. ‘The pyriform lobes are 
small and not protuberant. 
As previously stated, the cerebellum in all three specimens of 
the endocranial casts of Ictops is imperfectly preserved. On the 
posterior end of two of them portions of the cerebellar structures 
can be discerned. While a description of them is justified, a 
drawing of them in their imperfect state would be needless. The 
cerebellum of Ictops is simple and possibly primitive, though no 
more so than the cerebella of some modern mammals, notably 
Vespertillio. At first glance, this part of the brain seems divided 
into three vertical areas or lobes, but this is an appearance due 
to the manner of arrangement of the parts of the lobes. The 
cerebellum, as a whole, is more advanced than the cerebrum, 
since there are represented three major folds. The lobus anterior 
is evident in two specimens, but its limits are indistinct, save 
in one where the sulcus primarius is a prominent depression 
