414 C. JUDSON HERRICK 



prisingly constant and very simple. In this contribution I have 

 brought together certain features of embryonic and adult brains 

 of amphibians and reptiles which illustrate the fundamental sim- 

 plicity of this pattern 



Johnston has recently presented strong evidence that the tel- 

 encephalon must be regarded as the terminal segment of the 

 neural tube, a view confirming (with some modifications) the 

 original teachings of His as opposed to the usage in the BNA 

 tables In the latter the diencephalon is regarded as extending 

 to the extreme rostral end of the primary neural tube, thus com- 

 prising the whole of the unpaired ventricle of this part of the brain 

 and its lateral walls, including the lamina terminalis, while the 

 telencephalon is regarded as limited to the secondarily evaginated 

 parts of the neural tube termed the cerebral hemispheres, viz., 

 the lateral ventricles and their massive walls. The usage of 

 His and Johnston implies that the rostral part of the third ven- 

 tricle, bounded behind by the velum transversum above and the 

 chiasma-ridge (Johnston) below, and its walls are to be regarded 

 as telencephalon . medium, while the evaginated hemispheres con- 

 stitute the telencephalon laterale. Johnston has further shown 

 that in lower vertebrates there has been a progressive tendency as 

 we pass up the developmental series (both ontogenetic and phy- 

 logenetic) for more and more of the telencephalon medium to be 

 evaginated through the interventricular foramina into the hemi- 

 spheres. 



These considerations have an obvious bearing on the problem 

 of the relation of the cerebral cortex to the primordial tissues from 

 which it has been differentiated. With a view to the contribu- 

 tion of further data for the solution of this problem, I have ex- 

 amined the embryonic and adult brains of a series of types of 

 lower vertebrates, the first results of which are presented in this 

 paper. 



I shall discuss the brains of fishes only incidentally and devote 

 my attention chiefly to the amphibians and reptiles, whose cere- 

 bral hemispheres have evaginated so far from the primordial 

 neural tube as to present a form approximating more closely to 

 the mammalian conditions and readily leading up to them. 



