392 J. B. JOHNSTON 
Figs. 23-27 Ammoecoetes of Petromyzon dorsatus. Five sections from the 
sagittal series from which the model shown in fig. 8 was reconstructed. The 
outlines were made with the aid of the Edinger drawing apparatus. The velum 
transversum is seen as a distinct fold of the tela in figures 23 to 26, but in figure 
27 it joins the eminentia thalami. Figures 25 and 26 show well the course of the 
tract which runs up from the medial olfactory nucleus in front of the foramen 
interventriculare. This bundle may contain a tractus olfacto-corticalis and pos- 
sibly also the fornix column. The fibers of the commissural bundles beginning 
with the most rostral successively turn up into the primordium hippocampi (fig. 
24). The fibers which go laterally into the hemispheres are not readily seen in 
these sagittal sections because they are cut across. These sections show conclu- 
sively that the commissure is largely related to the primordium hippocampi. 
