RHINENCEPHALON OF DELPHINUS 507 
Early observers who pictured cetacean brains which exhibited 
absence of olfactory structures were Tiedemann (’26) and Stan- 
nius (746). 
The outside form of these cetacean brains is known from the 
works of several writers, the furrows especially having been 
discussed by Kiikenthal and Ziehen (’89) and Elliot Smith 
(02), among others. But sections have only twice been studied. 
In 1905, at the Baden Congress, Jelgersma read a paper on the 
results of his study of the brain of Phocaena, but this has never 
been published except by title. And also we have a very good 
description of the brain-stem of Delphinus by Hatschek and 
Schlesinger (’02), in which, however, the study of the forebrain 
and olfactory apparatus was outside of the special plan of their 
work. 
EXTERNAL OLFACTORY REGION 
The ventral surface of the dolphin’s brain (figs. 4 and 5) gives 
at first the impression that, though the olfactory tract and lobe 
are entirely absent, the lobus parolfactorius is still present in 
large size. One sees just in front of the chiasma, on either side, 
a large, somewhat oval, convex, protruding area, quite distinct 
in appearance from the substance of the frontal lobe. Broca, 
who was surprised to find no convolutions there, called it ‘lobule 
désert.’ This lies at a place where one finds in other mammals 
the lobus parolfactorius, and indeed, like this, it has behind it a 
typical substantia perforata anterior, as already described by 
Kikenthal and Ziehen. Frontally it is separated from the 
cortex of the frontal lobe by a depression which shows consider- 
able variation in extent and depth in the several brains examined. 
In one of the brains (fig. 4), it was very deep and showed as a 
continuous furrow. In another (fig. 5A) the depression was 
quite shallow and as a result the area did not appear so bulging. 
In a third, depicted in figure 5 B, there was a distinct furrow 
mesially, but this became less marked laterally. 
Laterally this area extends as a narrow grayish band, which 
disappears, getting narrower and narrower, in about the region 
where the nucleus amygdalae lies. This narrow grayish band 
THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 25, NO. 5 
