Cerebellum 57 



neurons, but in ordinary sections it appears to be composed 

 of only two distinct layers. The outer, or molecular layer, is 

 of a homogeneous or very finely punctate appearance, with 

 a few small cell-nuclei scattered through it. The inner, or 

 granular layer, on the other hand, is composed of cell-bodies 

 closely packed together. The outermost row of cells in this 

 layer is made up of very characteristic large, pyriform cells, 

 the Purkinje cells, of which the axons pass straight down into 

 the white matter, while the large, branched dendrites extend 

 out through the molecular layer. The dendrites of each 

 Purkinje cell spread out in a single plane sagittally placed, 

 i.e., at right angles to the axis of the cerebellar lamella. Each 

 dendrite is thus in a position to receive a maximum number 

 of stimuli from the numerous, fine fibres in the molecular 

 layer which run lengthwise of the lamella. 



The gray matter of the cerebellum, however, is not all 

 superficial in position. There are also certain masses im- 

 bedded in the deeper part of the white matter, near the roof 

 of the fourth ventricle (PI. IX.). Four pairs of these nuclei 

 are recognized, named in a medio-lateral direction respec- 

 tively nucleus fasti gii {nucleus tecti), nucleus globosus, nucleus 

 emboliformis, and nucleus dentatus {dentate nucleus or cere- 

 bellar olive). The dentate nucleus is a little larger than the 

 other nuclei and stretches out into the base of the stalk of 

 the floccular lobe. It is the ending-place of many of the 

 axons of the Purkinje cells, and the place of origin of most 

 of the fibres in the brachium conjunctivum. In the rat, this 

 nucleus is a compact mass slightly hollowed medially, so that 

 it appears somewhat curved in section. In man, the hollowing 

 has increased and the nucleus has grown as a whole until it 

 appears as a much-folded, pouch-shaped lamella, very similar 

 in form to the inferior olivary nucleus. This increase in 

 size of the dentate nucleus is apparently correlated with the 

 larger development of the cerebellar hemisphere. The three 

 remaining nuclei are proportionately larger in the rat than 



