424 



the superior and the posterior surfaces meet is about 110^ Towards 

 the inferior border the curvature of this surface diminishes. The postero- 

 inferior surface goes over into the antero-inferior surface, which is 

 turned towards the floor of the fourth ventricle. This surface is 

 about plane and shows, only on one side, the first trace of the fissura 

 fastigialis. 



The cerebellum, in this stage of development, is built up by three 

 different strata. The most internal of these layers, bounding the fourth 

 ventricle, is a matrix-layer (Fig. 1 M.). The nuclei of this stratum 

 are roundishly elliptic and arranged radially in respect of the ventri- 

 cular surface of the cerebellum. The thickness of this layer is variable. 



Along the rafe (Fig. 5) 

 the matrix is broad 

 and the nuclei lie closer 

 together than in the 

 adjacent parts of this 

 stratum. At the place 

 of attachment of the 

 tela chorioidea the ma- 

 trix reaches its greatest 

 diameter, where this 

 layer goes over upon 

 the taenia (Fig. 1, 6 T.), 

 by which the posterior 

 border of the cere- 

 bellum goes over into 

 the tela chorioidea. 



The matrix is con- 

 tinued into the inter- 

 mediate layer (Fig. 1 /.) 

 without definite limits. 

 This stratum forms the 

 bulk of the material 

 composing the cerebellum. The difference between the two strata lies 

 mainly in the filling up with nuclei which is not so dense in the inter- 

 mediate layer as in the matrix-layer. Neither is the radial arrange- 

 ment of the nuclei so obvious, though in most parts of the inter- 

 mediate layer, especially in the neighbourhood of the matrix, this 

 arrangement still prevails. The nuclei are mostly round and of the 

 same size as the nuclei of the matrix. 



In this intermediate layer originates a large system of fibres 



Fig. 3. Frontal section 3.3 mm distant from the 

 posterior border of the cerebellum. 15/1. Outline of a 

 photograph. Br.c. brachium conjunctivum. C. cere- 

 bellum. Isthm. isthmus. Mes. mesencephalon. Myel. 

 myelencephalon. T. taenia. T.ch.q. tela chorioidea of 

 the fourth ventricle. V.q. fourth ventricle. 



