102 THE BRAIN OF THE TIGER SALAMANDER 



abundant. The deep neuropil of the alba contains an elaborate sys- 

 tem of association fibers, which has been described in detail (figs. 

 Ill, 113; '336, p. 194; '33e). The intermediate neuropil contains 

 many of the recognizable long tracts, and in the striate area it is 

 elaborately developed, as already described. Superficially of the stri- 

 ate neuropil is a strio-amygdaloid neuropil, which is continuous 

 dorsally with the piriform and dorsal neuropil. This sheet as a whole 

 is evidently the synaptic field of the pallial associations. It receives 

 the dendrites of the underlying gray substance but contains no cell 

 bodies. In higher animals this synaptic zone seems to exert a neuro- 

 biotactic influence, so that in embryonic stages all the neurons of the 

 pallial field migrate outward and are incorporated within it, thus 

 producing the laminate cortex. 



In the amphibian primordium hippocampi, this movement has be- 

 gun but is not consummated. The deep gray layer has been broken 

 up, and its elements are dispersed. The periventricular neuropil of 

 the grisea and the neuropil of the alba merge, so that the entire area 

 is pervaded by a dense entanglement of dendrites and axons, within 

 the meshes of which the cell bodies are imbedded. This neuropil is 

 denser in two places — rostrally and ventrally, where subpallial con- 

 nections predominate, and dorsally, where pallial associations pre- 

 dominate. In the reptiles, with differentiated cortex, the correspond- 

 ing two parts of the hippocampal cortex are structurally different. 



In Necturus the most rostral fascicles of the strio-pallial associa- 

 tion go far forward and dorsally above the posterior end of the 

 olfactory bulb to reach the dorsolateral sector of the anterior olfac- 

 tory nucleus and territory adjacent to it (fig. 111). This is clearly a 

 secondary olfactory nucleus of subpallial type, adjacent to the olfac- 

 tory bulb and traversed by the great dorsolateral olfactory tract, 

 from which it receives numberless terminals and collaterals. Its prin- 

 cipal discharge is. backward into the primordium pirif orme, a pallial 

 area (fig. Ill, tr.ol.pal.L). These connections would, perhaps, have 

 no special significance in themselves, but comparison with reptiles 

 shows that there the corresponding region exhibits remarkable pe- 

 culiarities. In urodeles the area in question is one of the least dif- 

 ferentiated parts of the hemisphere, except for the strong fascicles of 

 the strio-pallial association, and perhaps this lack of specialization 

 favors the role which it seems to play as germinative tissue for 

 neopallial cortex. 



Cortex of simple pattern is present in turtles in each of the three 



