Exxiior Smitu, Lran of Archeocet.. 49 
large mammalian body, even if the cerebrum is small. I cannot 
offer any more satisfactory explanation of the magnitude of the 
cerebellum in Zeuglodon than this, 
It is clear from the foregoing that the extraordinarily great 
contrast in the appearance of the brain of the Archzoceti and 
that of the Cetacea cannot be urged as a reason against their 
kinship, when it is remembered that the operation of known 
factors is quite sufficient to explain the transformation of the 
one type into the other in the time which has separated the 
Eocene period from the present. 
Having disposed of these negative arguments, we may 
consider the positive evidence for Cetacean affinity in the brain 
of Zeuglodon. 
The shape of the cerebrum, and especially its relatively 
great breadth, is peculiar. In fact, this form of hemisphere 
rarely or never occurs among mammals, other than the Cetacea. 
I have elsewhere’ attempted to explain the shortness of the 
Cetacean hemispheres by the fact that the abortion of the basal 
(olfactory) parts of the cerebrum limits their longitudinal ex- 
tension. This, however, is not the whole explanation, because 
in many microsmatic Sirenia (Za/icore), and Pinnipedia (Osaria, 
Phoca), the hemispheres are not especially broad. The dispro- 
portionate breadth seems, in fact, to be to some extent a char- 
acteristic cf the Cetacea; and, in this respect, Zeuglodon agrees 
with them. 
The peculiar elongation of the olfactory peduncles be- 
yond the anterior extremities of the hemispheres is rarely found 
in mammals, though it is common enough in Reptiles and the 
Ichthyopsida. In fact, the exact parallel to the condition found 
in Zeuglodon occurs among recent mammals only in the Cetacea.* 
An analogous condition is found in the extinct Lemuroid 
Megaladapis [described by ForsytH Major (of. cét.)] and some 
Amblyopoda. 
1 ‘Catalogue of the College of Surgeons,’ of. czt., p. 350. 
* Full references to this are given by ForsyrH Major, ‘‘On the Brains of 
Two Sub-Fossil Malagasy Lemuroids,” ‘Roy. Soc. Proc.’ vol. 62, 1897, p. 48, 
second footnote. 
