C. Judson Herrick 



Comparison with Amphibia. 



In the comparison of the telencephalon of fishes with that of Amphi- 

 bia some landmarks can be recognized with great clearness, but other 

 points are more puzzling. From the descriptions of Elliot Smith (1908) 

 and Holmgren (1922) it is very probable that the Dipnoi present the 



clearest evidence of the mode of transi- 

 tion from the unevaginated telencephalon 

 médium oí primitive type to the evagina- 

 ted cerebral hemispheres of amphibian 

 type fcf. Herrick, 192IJ. But until more 

 is known of the functional connections 

 and embryology of these dipnoan brains 

 it is not profitable to discuss the apli- 

 cation to this group of animáis of the 

 functional factors here under considera- 

 tion. The larvae of urodele Amphibia 

 become functional at a very early stage 

 and it is hoped that studies now in 

 process on the sequence of matura- 

 tion of their fiber tracts in correlation 

 with the morphogenesis of the he 

 mispheres and the development of 

 reflex patterns will shed further light 

 upon these problems. 

 In the adults of lower Amphibia most of the telencephalon is fuily eva- 

 ginated into the cerebral hemispheres, but there is always a residue left in 

 the telencephalon médium (fig. 30). This residue includes the nucleus 

 preopticus and in some cases variable proportions of the imperfectly diffe- 

 rentiated área olfacto-somatica (amygdalo-striate complex). l^he entire 

 hemisphere is reached by fibers of the tractus olfactorius, except pe- 

 rhaps the posterior ends of the amygdalo-striate complex and of the pri- 

 mordium hippocampi. The subdivisión of the hemisphere of Amblys- 

 toma and some of the non-olfactory functional connections are shown 

 diagrammatically in figures 31 and 32. In these figures on the left are 

 the conventional markings indicating áreas corresponding to those of 

 the fishes described in the preceding pages. 



Fig. 30. — Diagrammatic longitu- 

 dinal section of the forebrain of 

 an amphibian, for comparison 

 with figures 1,7, 12 and 19. The 

 larger part of the telencephalon 

 has been evaginated to join the 

 olfactory bulbs in the formation 

 of the hollow cerebral hemisphe- 

 res, whose walls are nowhere 

 greatlv thickened. 



