422 C. JUDSON HERRICK 



tral divisions of the tractus olfactorius medialis. The ventral 

 niedullated tract arises only from the rostral end of the bulb. 

 All of its fibers, which are few in number, terminated soon in the 

 nucleus olfactorius anterior. The extent of distribution of the 

 unmedullated fibers I have not determined, for the dorsal division 

 enters the rostral end of the primordium hippocampi where its 

 fibers are mingled with those of the fimbria complex and the ven- 

 tral division is mingled with the median forebrain tract. 



The tractus olfactorius dqrso-lateralis arises from the whole 

 length of the dorsal border of the olfactory bulb. The total 

 number of niedullated fibers is, accordingly, quite large (figs. 8 

 to 11). These niedullated fibers are, however, all short, ending 

 in the adjacent gray of the nucleus olfactorius anterior and pars 

 dorso-lateralis of the hemisphere. The niedullated tract does 

 not increase in size as we approach the caudal end of the bulb 

 and all its fibers terminate a short distance farther caudad (fig. 

 12). The accompanying unmedullated fibers doubtless extend 

 farther caudad and reach the posterior pole as in the larva and 

 the Anura, though my preparations do not demonstrate this in 

 adult Amblystoma. 



The tractus olfactorius ventro-lateralis arises from the caudal 

 end of the olfactory bulb (corresponding with the bulbulus ac- 

 cessorius of the frog) and, as in the frog, passes directly back close 

 to the ventricular ependyma to end in a cellular thickening at the 

 caudal end of the pars ventro-lateralis opposite the anterior com- 

 missure, which corresponds with the so-called corpus striatum 

 of the frog. 



As we approach the caudal end of the olfactory bulb (fig. 11) 

 the medial wall of the hemisphere becomes . specialized into two 

 structurally defined regions, the primordium hippocampi above 

 and the nucleus post-olfactorius below, the latter corresponding 

 to the eminentia post-olfactoria (Gaupp) of the frog brain and 

 probably to the tuberculum olfactorium of mammals. The dor- 

 sal wall remains undifferentiated and is continued caudad into 

 the pars dorso-lateralis of the hemisphere. The latter is, accord- 

 ingly, to be regarded as the direct continuation of the nucleus 

 olfactorius anterior. 



