378 J. B. JOHNSTON 
Fig. 7 Lampetra. Dorsal view of the model shown in figure 5. This is pre- 
sented chiefly to illustrate the stem-hemisphere fissure and the wedge-shaped 
telencephalon medium. The attached border of the tela chorioidea is drawn. 
Its caudo-lateral angle is the upper end of the recessus praehabenularis. In 
Petromyzon dorsatus the eminentia thalami comes up nearly to this point and the 
velum transversum is attached to it. The broken line running caudo-laterad 
from this point corresponds to the plane of sudden transition in internal structure 
from the primordium hippocampi to the pretectal and subhabenular region. 
