LECTURES ON THE CENTRAL NERVOUS SYSTEM. 



Even in the case of the amphibians, where two large, flat 

 hemispheres, of an oval shape, spring from the primary fore- 

 brain vesicle, their wall, composed of an outer layer of glia and 

 an inner granular layer, contains only few and irregularly-dis- 

 , tributed ganglion-cells. In reptiles jye_. first meet with a deposit 

 | of pyramidal cells, disposed in several layers and covering most 

 of the surface, a true brain-cortex. 



FIG. 13. 

 Sagittal median section through the brain of a bony fish. 



This is most extensively developed in the median wall, and 

 there are grounds for believing that this, the lowest cortical 



...in. 



* : 



FIG. 14. 

 Amphibian brain. Diagram of a sagittal section. 



Hinlerhirn, After-brain. Miltelhirn, Mid-brain. NacJih., After-brain. 



formation, is the representative of the cornu ammonis in mammals 

 (origin of the fornix, etc.). From this point on, the development 

 of the fore-brain takes place in two different ways. In birds the 

 corpus striatum attains a relative size and complexity found in 

 no other class of animals, while the formation of cortex does 

 not much increase. In mammals, however, the pallium, with 

 its cortical 'layer, becomes a large structure, which causes the 



