FOREBRAIN MORPHOLOGY 417 
In the subpallial region of the forebrain the whole ventral part is 
covered by a distinct tuberculum olfactorium (t.olf.). Behind 
the pallial portion the tuberculum olfactorium ascends laterally 
on the brain as far as to the stria medullaris. Caudally, the 
tuberculum olfactorium ends at the posterior margin of the second 
‘striatal’ swelling (‘striatum’ of Kappers and Carpenter), where 
the nucleus preopticus begins. 
Dorsal to the medial border of the tuberculum olfactorium 
lies the medial septal nucleus (figs. 24 to 27, n.m.s.). This 
nucleus never enters the ‘septal’ portion of the evaginated fore- 
brain. The nucleus lateralis septi is rudimentary. No cellular 
fimbrial portion of this nucleus is present. A ‘sulcus septalis’ is 
present (figs. 25, 26, s.s.). 
Making exception of some special characters, such as the elon- 
gation of the telencephalon medium and the striatal swellings, the 
ehimaeroid forebrain exhibits some conditions which place this 
type on a lowlier phylogenetic stage than the selachian, approach- 
ing that of the cyclostomes. Such a primitive character is 
that the hemispheres are not confluent with each other, but only 
joined by a chorioidal tela. Also the lack of a nucleated fimbrial 
portion of the subpallial septum is a primitive character. 
DIPNOI 
My sectioned material of dipnoan brains being not more than 
a frontal and a horizontal series of young Protopterus annectens, 
stained with iron-haematoxylin, I was not able to make any 
original studies on these animals, beyond the determination of 
the nuclei. I have found in Protopterus the same conditions as 
those already found by Elliot Smith in Lepidosiren.’ I have but 
5 The forebrain of Ceratodus seems to be built up in principle in the same way 
as in Protopterus and Lepidosiren. In the last number of this Journal that has 
reached me (vol. 32, no. 4), however, Herrick has pointed out some very great 
differences between Ceratodus and the other dipnoans, but examining two 
transverse series of Ceratodus brains I failed to recognize these differences, 
quoted by Herrick from Bing and Burckhardt (’05). Herrick says: ‘“The lateral 
outpouching . . . . extends but little, if at all, rostrally of the terminal 
plate and there is no sagittal fissure separating two cerebral hemispheres behind 
the olfactory bulbs. The true (fully evaginated) cerebral hemisphere, 
accordingly, contains only the olfactory bulb.’’ In my specimens there is a 
