THE TELENCEPHALON IN CYCLOSTOMES 349 
Behind the eminentia thalami isa ridge extending from the nucleus 
habenulae to the interpeduncular region and occupied by the 
tractus habenulo-peduncularis. Between this ridge and the emi- 
nentia thalami is a sulcus diencephalicus medius which is some- 
what more regular than in Lampetra. The sulcus limitans of His 
is somewhat less pronounced than in Lampetra. 
Professor Herrick thought that he found in Ichthyomyzon con- 
ditions which supported his theory regarding the division of the 
diencephalon and the telencephalon of amphibians into four lon- 
gitudinal columns. In amphibians (Herrick, ’10,p. 419) the sulcus 
medius forms the dorsal boundary of the eminentia thalami and 
runs caudally toward the tuberculum posterius. The statement 
that this sulcus and the sulcus ventralis “converge anteriorly to 
the interventricular foramen’ is evidently without foundation, 
since the sulcus medius is situated dorso-caudal to the eminentia 
thalami and the velum transversum, and can not reach the inter- 
ventricular foramen. In the amphibians studied by the writer 
(Amblystoma, Necturus, Cryptobranchus, Rana, Bufo) the suleus 
medius runs up into the dorsal sac and has no relation to the inter- 
ventricular foramen. This fact is clearly shown also in Herrick’s 
figures 5, 18, 19, 22, 33 and 34. 
In Herrick’s Ichthyomyzon figures 78, 79 and 80, the s.m. cor- 
responds to my sulcus limitans hippocampi, while in figure 81 
and on the right side of figure 80, s.mm. is the sulcus hypothalamicus. 
Consistent with his indentification of this with the sulcus medius, 
Herrick labels the area below it as the pars ventralis thalami and 
compares it with the eminentia thalami of amphibians (’10, p. 
471). This interpretation is obviously untenable, since the 
eminentia thalami of amphibians is caudo-dorsal to the inter- 
ventricular foramen, immediately adjacent to the nucleus habe- 
nulae, is bounded below by the sulcus diencephalicus ventralis 
and is traversed by the compact stria medullaris just before this 
bundle enters the nucleus habenulae. See Herrick’s figures 17— 
to 22. The true position of the eminentia thalami in Ichthyomy- 
zon 1s Clear from Herrick’s figures 80 and 81 in which the compact 
stria medullaris is about to enter the nucleus habenulae. These 
figures show that the eminentia thalami lies as in amphibians at 
