262 THE RHOMBENCEPHALON. 



point of the roof, nucleus fastigii (Stilling!). ' In the last two the 

 stellate cell-bodies are larger than in the nucleus emboliformis 

 or dentatus; but, otherwise, they are alike in structure. The 

 nucleus fastigii and nucleus globosus form a part of the origin of 

 the acustico-cerebellar tract, which descends to the nucleus of 

 Deiters in the medulla; probably axones of Purkinje's cells also 

 enter into the acustico-cerebellar tract in man, as they do in the 

 cat (Clarke and Horsley). Perhaps the nucleus emboliformis 

 and nucleus dentatus have a less important connection with the 

 same tract. The small cerebellar ganglia, and especially the 

 nucleus fastigii and nucleus globosus, constitute a relay in the arc 

 of equilibrium. 



The White Substance of the Cerebellum (Figs. 79 and 81). 

 The corpus medullare contains all the white matter of the cere- 

 bellum. It is a strong body measuring a third of an inch in thick- 

 ness vertically in the middle of the hemisphere, but in the worm 

 it is a thin sheet and is very slender as seen in median section. 

 Its branches to the cerebellar gyri are called the medullary lamina 

 (lamina medullares}. Viewed in a sagittal section of the hemis- 

 phere, the medullary laminae are short and stubby branches of a 

 very thick trunk; but the tree-like appearance of the medullary 

 body and laminae in the vermis is perfect, hence the name, arbor 

 vita, which is applied to them there. In the anterior cerebellar 

 notch the medullary body divides into a thick superior lamina 

 and a thin inferior lamina which are separated by a transverse 

 furrow, the bottom of which constitutes the peak, or fastigium, 

 of the fourth ventricle. The inferior lamina is the inferior med- 

 ullary velum, already described; this, with the continuation of its 

 ependymal epithelium, forms the roof of the inferior half of the 

 fourth ventricle. The superior lamina of the corpus medullare 

 forms the three pairs of connecting bands (peduncles) and the 

 superior medullary velum. Medullated axones make up the 

 entire corpus medullare and its divisions. We study these axones 

 in three systems like those of the cerebrum: 



I. Projection, or peduncular fibers. 

 II. Commissural fibers. 



III. Association fibers. 



