716 THE yERVOUS SYSTEM 



on the right side will expose the plicated bag of grey matter which constitutes the nu(_-lfus, an 

 opening into which, the hiluiu, will be seen on the inner and ujtper side. If a small portion of 

 the fibres of the superior peduncle of the cerebellum of the same side be now raised and torn 

 gently in a downward direction, the fibres are readily traceable into the white centre of the 

 nucleus. 



A horizontal section through the superior vermis will show the smaller nuclei of the cerebel- 

 lum (nuclei fastigii, embuliformis, and globosus). These are, however, somewhat difficult to find. 

 Lastly, a median sagittal section will expose the fourth ventricle, to obtain a good view of which 

 the remainders of the cerebellar hemi.spheres should be drawn gently aside. In doing this care 

 should be taken of the inferior medullary velum. 



White matter of the cerebellum. — In a mesial sagittal section of the cere- 

 bellum (fig. 427) the amount of white matter is smaller in proportion to the grey 

 matter than in any other section. It ])resents a characteristically branched appear- 

 ance which is called the arbor vitae. Two main divisions, the vertical and 

 horizontal branches, of the arbor vittc are described, and from these secondary 

 ramifications arise. The vertical branch is mainly continued into the culnien, 

 Avhere it sul)divides somewhat freely. It sends forwards usually two branches into 

 the lol)ulus centralis, and a slender twig into the lingula. The main axis of the 

 horizontal branch is prolonged into a slender white band, which enters the folium 

 cacuminis. From the upper surface of the horizontal branch a stout oft'set is sent 

 into the declive, and from its lower surface branches are sent into the tuber val- 

 vula?, pyramid, and uvula. A small offset enters the nodule, and if this be traced 

 in a lateral direction it will be found to be continued into the inferior medullary 

 velum. 



In coronal sections the disposition of the white matter in the hemispheres is 

 well seen. It forms a somewhat ovoid mass in each hemisphere, near the centre of 

 which the corpus dentatum is placed (fig. 416). The appearance is very similar in 

 sagittal sections through the centre of a hemisphere. It is not necessary to give a 

 separate description of the divisions of the white matter, as these correspond to the 

 lol)ulation of the surface. 



The grey matter in the interior of the cerebellum consists of four pairs of 

 nuclei, Avhich are everywhere separated Ijy Avhite matter from the grey matter of the 

 folia. The largest of these nuclei in each hemisphere is called the corpus dentatum. 

 The smaller, which are placed nearer the middle line, are called the nucleus emboli- 

 formis, nucleus glolwsus, and nucleus fastigii. 



The corpus dentatum is a crumpled sheet of grey matter which presents a 

 similar outline in coronal, sagittal, and horizontal sections. This outline is 

 approximately an oval bounded by a wavy line. This line is broken only on the 

 inner and anterior side, where the white matter of the exterior is continuous with 

 that of the interior through an aperture called the hilum. 



Tin- nucleus emboliformis is an elongated streak of grey matter, which is 

 placed on the inner side of the corpus dentatum. It is somewhat enlarged at its 

 anterior extremity, hence it may be descrilx'd as club-shaped. The nucleus glo- 

 bosus consists of several s^jheroidal clumps of grey matter, which are ])laced on the 

 inner side of the preceding; these clumps are connected with one another, and also 

 Avith the nucleus emboliformis and nucleus fastigii. The nucleus fastigii varies 

 somewhat in its minute structure from the three nuclei above described. It is 

 situated innnediately over the roof of the fourth ventricle, separated from that 

 cavity, however, by a thin stratum of white matter. The nuclei of opposite sides 

 nearly touch one another in the middle line. 



The fibres of the cerebellum may be described under the following heads: 

 (rt) Fibres derived from the cerebellar peditncles, and (b) intrinsic fibres, (a) The 

 fibres of the middle peduncle connect the cerebellum (1) Avitli the miclei of the 

 l)ons on the same side, (2) with the i)Osterior longitudinal Imndle and the fillet of 

 the same side, and by means of these tracts with the corpora quadrigemina, and 

 the antero-lateral tract of the spinal cord, (3) with the pyramidal tracts of the 

 same and the opposite side by means of wbich connections are established with 

 the corpora quadrigemina and the corpus striatum. The upper fibres of the 

 pons pass into the lateral parts of the cerebellar hemispheres, and end in the grey 

 cortex. The middle fibres sweep dowiiAvards, fornung tlie oblique fasciculus, 

 and end in the folia of the inferior surface. The lower fibres accom]tany the 



