190 C. Judson Herrick 



and dorsal áreas are not distinct at the rostral and caudal ends of the 

 hemisphere. Between these undifferentiated regions tissue which is 

 clearly primordium hippocampi is differentiated in the dorso-medial wall, 

 but the dorso-lateral convexityof the hemisphere shows no clear boundary 

 between pallial and subpallial parts. The whole lateral wall receives 

 fibers of the tractus olfactorius. The ventro-lateral wall contains the 

 massive lateral forebrain bundle, w^iose connections determine its func- 

 tional interpretation. 



The ventro-lateral wall is the direct forward extensión of the pars ven- 

 tralis thalami, with which it is broadly connected by the lateral forebrain 

 bundle. It receives ascending somatic projection fibers from the pars 

 dorsalis thalami (tractus thalamo-frontalis) and discharges strio-thalamic 

 fibers into the ventral thalamus. These connections identify it with the 

 área somática of fishes; but the homology is incomplete, for this same 

 región is connected with the hypothalamus by the olfactory projection 

 tract oí Cajal, which is the amphibian equivalent of the tractus pallii, and 

 it also receives fibers of the tractus olfactorius. In short, the ventro-lateral 

 quadrant of the hemisphere is an olfacto-somatic correlation center 

 with hypothalamic connections. It corresponds topographically with the 

 intermedíate zone of the telencephalon as defined in fishes, but its functio- 

 nal composition is different. Rostrally it contains the ventral part of 

 the área olfactoria lateralis and caudally the área somática, but these are 

 nowhere completely separated. It has also taken up a considerable part 

 of the hypothalamic connection represented in the tractus pallii of fishes. 



The dorso-lateral convexity of the hemisphere includes dorsally a 

 portion of the área olfactoria dorsalis which has not assumed the differen- 

 tiation characteristic of the primordium hippocampi on the medial wall, 

 and laterally this passes over with no sensible boundary into the área 

 olfactoria lateralis. This dorso-lateral región receives the very strong 

 tractus olfactorius dorso-lateralis, termináis of the olfactory projection 

 tract, and of the ascending projection fibers from the dorsal thalamus 

 (tractus thalamo-frontalis). 



This is the condition in the lower Urodela. In the higher Urodela 

 like Amblystoma (figs. 31, 32) a sharp ventricular sulcus (s. a. d.) has 

 appeared at the dorsal angle ofthe hemisphere separating the medial 

 primordium hippocampi from the dorso-lateral quadrant of the hemis- 

 phere. But there is no well defined boundary between the latter quadrant 



