13? 



ventricle (Fi(?.'=!l, p. v.). The enrlier Hiritoaiists had observed 

 the pressace of these elevations in certain selachian fore- 

 brains, but their place in the organization of the palliarn has 

 not been recognized heretofore. A pallial eminence is the 

 seat of a crowded group of neurones, and the elevated condi- 

 tion of the mass has probably arisen from the disproportion- 

 ately rapid growth which occurs here. 



The superficial zone of a pallial eminence is occupied 

 almost exclusively by axis-cylinders, the significance of which 

 will be noticed presently. The neurones lie in a crowded aggre- 

 gate just vit^in. Pig. 39 shows a representative group of these 

 neurones. They are seen to embrace several varieties of form 

 and size, all disposed without arrangement into definite layers. 



a. neurones of the Tr-aotus Pallii. — The external feat- 

 ures of the largest variety of neurone of the pallial eminence 

 will be seen by referring to F'ig.39. This type assumes a vari- 

 ety of guises, but it is characterized by its larger size and 

 by the fact that its axone enters the tractus pallii. The 

 cell-body of such a neurone ranges from broadly oval to dis- 

 tinctly polygonal in forn. The dendrites are long and widely 

 spreading processes, arising through thick basal masses at 

 three or four almost equidistant points. A dendrite branches 

 once or twice, dichotomously as a rule, and the terminal 

 lengths become quite slenier. Its surface is slif^htly rough- 

 ened by minate ^emmules. These are far less conspicuous, how- 



