THE CEREBELLUM. 517 



on every side, the distinct lamellation of the medulla of the 

 cerebellum when its fibres are separated. 



2. The dentated nuclei, discovered by Vieussens, form infe- 

 rior grey medullated, and in Man contorted, laminae, having 

 a thickness of 0'3 of a millimeter, lying near that surface of 

 the cerebellum which overlaps the fourth ventricle, the con- 

 tained medullary substance of which enters it by a hilus 

 directed downwards and inwards. Their fine dentations ex- 

 hibit in Man the most remarkable similarity to the inferior 

 olivary body, which they also resemble in the cellular 

 elements they contain, which are 30 p long, and 12 /m thick. 

 I distinguish the presence also, in Man, of secondary dentated 

 nuclei, which are of smaller size, but are composed of a thicker 

 grey lamina, measuring 06 of a millimeter, situated somewhat 

 below and in front of the former, and containing larger ele- 

 ments (having a long diameter of 45 p, and a breadth of 15 /*) 

 Their sinuosities are l&ss fine and close than the principal 

 dentated nuclei, and the continuity of the curves is frequently 

 interrupted by the passage through them of strong medullary 

 fasciculi. In Mammals (as in the Quadrumana, fig. 255, D D), 

 the nucleus no longer possesses the beautifully marked ap- 

 pearance, the delicate curvatures, of that of Man, but is dis- 

 tended by the introduction of a considerable quantity of 

 connective tissue into its interior, and forms a simple mass of 

 grey substance, with a sinuous outline. 



3. The roof nuclei (Dachkerne), discovered by Stilling, are 

 two convex and, when seen from above, rhombic masses, which 

 in the cerebellum of Man are situated below the central 

 lobule of the superior vermiform process, and have a length 

 and breadth of about five millimeters, and a height of two milli- 

 meters. Their connections may be exposed by careful dis- 

 section ; and they are then found to be separated from one 

 another by a thin median medullary layer, and to be traversed 

 by a considerable quantity of medullary substance. They 

 contain long slender nerve cells, which are provided with thick 

 processes, and have a length of 60^, and a thickness of 15// 

 or more, corresponding therefore in size with those in the 

 external auditory nucleus (fig. 255, T). 



Our knowledge of the course of the medullary fibres of the 



