384 J. B. JOHNSTON 
oe 
Cine 
_ 
Fig. 16 The third section of the same series. Note the extreme difference 
in size between the two nuclei habenulae and the passage of the first stria medul- 
laris fibers as a compact bundle over to the right nucleus. The prehabenular 
recess is narrow in Lampetra and the eminentia thalami does not appear as a dis- 
tinct ridge in these dorsal sections. This is due to the large size of the primordium 
hippocampi in Lampetra as well as to the crowding together on account of the 
pressure of the buccal funnel. A section through the brain of Ichthyomyzon or 
Petromyzon dorsatus at this same level would show a distinct eminentia thalami. 
Compare figures 6 and 9. 
