266 Journal of Compahatuk Neurology. 



brates, yet in its internal structure it differs but little from 

 the adult mammalian cerebellum. As in the mammalia, so 

 here, the epencephalon consists of three major histological 

 regions; the epithelium, the cerebellar cortex, and the body. 

 Around the periphery, lining the convolutions, we find 

 the narrow epithelial layer; entad to this we find the 

 cortex, while further entad, forming the core, we find the 

 body. 



Cerebellar Cortex (Plate XVIII, Fig. 6). — The transversely 

 and unequally convoluted cerebellar cortex is composed of 

 three laminae. The most ectal lamina is the widest of all. It 

 is composed of neuroglia through which are scattered a few 

 of Deiter's corpuscles. The second lamina is very narrow. It 

 consists of a single layer of the well-known Purkinje's cells. 

 These are large and gibbous flask cells. In hsematoxylin 

 and aluminium-sulphate cochineal preparations, these cells 

 are densely stained and present large, clear, spherical nuclei 

 and large, dense nucleoli. In different brains the size of 

 these cells varies greatly, but in all cases they rank with the 

 largest cells in the brain. The width of the next layer is a 

 variable quantity. This dimension varies not only in differ- 

 ent brains, but also in different parts of the same epenceph- 

 alon. But, in every epencephalon, the major local thicken- 

 ings of this lamina take place in a definite and constant 

 manner. In all cases this layer is narrowest at the proximal 

 extremity of each canvolution. Thence the width in- 

 creases gradually, although irregularly, until the distal ex- 

 tremity of the convolution is reached. There the layer is 

 widest. Although at the proximal extremity of each convo- 

 lution this layer is often but little wider than the layer of 

 Purkinje's cells, yet at the distal extremity of each convolu- 

 tion it will be almost as wide as the external neuroglia layer 

 (Plate VII, Fig. 4; Plate XIV, Fig. 8). This fact seems to 

 warrant the following suppositions: 



I. This layer of the avian epencephalon was deposited 

 before that bbdy became convoluted. 



