446 C. JUDSON HERRICK 



to the columna fornicis (see p. 423) pass downward into the septum 

 from amongst these cells, but I have not been able to establish 

 their connection with them. If this connection exists, then these 

 cells constitute a true cortex hippocampi. The superficial layer 

 of tangential cells can be easily distinguished from the deeper 

 cells in sections stained with toluidin blue on account of their 

 difference in form, which is shown diagrammatically in fig. 40. 

 There is, however, no cell-free medullary or molecular laj-er be- 

 tween these cells and the so-called pyramidal cells which fill the 

 remainder of the primordium. 



In addition to the true columna fornicis fibers which pass down 

 through the septum and lamina terminalis in the typical verte- 

 brate way, as described above, there are other connections which 

 are functionally of the same type. Unmedullated fibers from all 

 parts of the primordium hippocampi and from the dorso-lateral 

 part (the latter curving around the dorsal and mesial surface 

 of the hemisphere) pass downward into the nucelus medianus 

 septi. Some of these form one component of the complex tract 

 known as the tractus olfactorius septi and may pass through this 

 nucleus to enter the hypothalamus by the way of median fore- 

 brain tract, in which case they should be associated with the 

 medullated tract already described as columna fornicis. Others 

 certainly end within the nucleus medianus. Since the latter 

 sends its fibers to the hypothalamus, this path with its interpolated 

 synapse may also serve functionally the same purpose as the 

 columna fornicis. No fibers pass from the true columna fornicis 

 into the stria medullaris, as in reptiles and mammals, to form the 

 tractus cortico-habenularis ; but there are other connections which 

 functionally belong to the fornix system. 



Some of the characteristic relations of the rostral part of 

 the hemisphere are shown in the diagrammatic cross section, 

 fig. 40. 



In no Amphibia do the fibers of the commissura hippocampi 

 system take the course characteristic of the reptiles and mammals, 

 viz., above the interventricular foramen, to cross in the lamina 

 terminalis in front of the foramen; on the other hand, they cross 

 behind the foramen by two paths. One of these is ventral in the 



