574 



MEDULLARY STRUCTURE OF THE CEREBELLUM. 



portion of the superior vermifonTi process is elevated, and is 

 called the monticulus. 



— When viewed from above, the two hemispheres externally 

 appear circular, and at the place where they are joined to the 

 central portion are deeply notched before and behind. Hence 

 they form two fissures in tl>e median line ; one looking towards 

 the cerebrum, and receiving the tubercula quadrigemina, g, fig. 

 225, termed the semilunar fissure : the other backwards, 

 receiving the falx cerebelli, and is called the purse-like fissure, 

 from its narrowness at first, and its subsequent enlargement. 

 Reil, employs the term horizontal or lateral fissures, to desig- 

 nate those depressions which extend transversely across the 

 fore part of the cerebellum, and contain the processes or parts 

 of its crura passing to the pons varolii.* 



— These fissures are continuous with the intervals between 

 the upper and under posterior parts of each hemisphere, which 

 extend as far as the purse-like fissure. Thus a deep furrow may 

 be traced all round each hemisphere dividing the cerebellum into 

 an upper and under portion. Each hemisphere has five lobes, 

 two on the upper, and three on the under surface ; these are 

 separated from each other by deep furrows or fissures, which 

 pass in to the central medullary nucleus, as seen in fig. 225, in 

 which is represented a vertical section of one hemisphere. 

 — Each one of these lobes, is subdivided, as we may see, into 

 a nun)ber of lobules, by a series of smaller furrows. These 

 are found on the periphery of the lobes, and on the sides of 

 the large fissures which separate the lobes from each other, and 

 each one of these lobules again is formed of a number of hori- 

 zontal leaflets. Each leaflet is composed of a folded layer of 

 cineritious neurine half a line thick on its outer side, and of a 

 medullary layer within. The cineritious coverings of the leaf- 

 lets are all continuous together, so that each hemisphere of the 

 cerebellum has a cortical covering of cineritious matter, with a 

 superfices equal to that of a sphere twenty inches in diameter, 

 but plaited and folded up in a compact mass, to suit the narrow 

 space in which it is lodged in the cranium. 



^ * Reil, Mayor's Translation, Anat. and Med. Commentaries. 



