STRUCTURE OF CEREBELLUM. 



533 



The gray matter in the floor of the ventricle consists of a tolerably thick 

 stratum, continuous below with the gray commissure of the cord, and extending 

 up as high as the aqueduct of Sylvius, besides some special deposits connected 

 with the roots of origin of certain nerves. In the upper half of the ventricle is 

 a projection situated over the nucleus, from which the sixth and facial nerves 

 take a common origin. In the lower half are three eminences on each side for 

 the roots of origin of the eighth and ninth nerves. 



Structure. If a vertical section is made through either hemisphere of the cere- 

 bellum, midway between 



its centre and the superior Fig. 272. Vertical Section of the Cerebellum, 



vermiform process ; it will 

 be found to consist of a 

 central stem of white mat- 

 ter, which contains in its 

 interior a dentate body. 

 From the surface of each 

 hemisphere, a series of 

 plates of medullary matter 

 are detached, which, co- 

 vered with gray matter, 

 form the laminae ; and from 

 its anterior part arise three 

 large processes or pedun- 

 cles, superior, middle, and 

 inferior, by which it is con- 

 nected with the rest of the 

 encephalon. 



The laminse are about 



ten or twelve in number, including those on both surfaces of the cerebellum, those 

 in front being detached at a right angle, and those behind at an acute angle ; as 

 each lamina proceeds outwards, other secondary laminae are detached from it, and, 

 from these, tertiary laminae. The arrangement thus described gives to the cut 

 surface of the organ a foliated appearance, to which the name arbor vitse has been 

 given. Each lamina consists of white matter, covered externally by a layer of 

 gray substance. 



The white matter of each lamina is derived partly from the central stem ; in 

 addition to which white fibres pass from one lamina to another. 



The gray matter resembles somewhat the cortical substance of the convolutions. 

 It consists of two layers, the external one, soft and of a grayish color, the internal 

 one, firmer and of a rust color. 



The corpus dentatum or ganglion of the cerebellum is situated a little to the inner 

 side of the centre of the stem of white matter. It consists of an open bag or 

 capsule of gray matter, the section of which presents a gray dentated outline, 

 being open at its anterior part. It is surrounded by white fibres ; white fibres 

 are also contained in its interior, which issue from it to join the superior peduncles. 

 The peduncles of the cerebellum, superior, middle, and inferior, serve to connect 

 it with the rest of the encephalon. 



The superior peduncles (processus e cerebello ad testes] connect the cerebellum with 

 the cerebrum ; they pass forwards and upwards to the testes, beneath which they 

 ascend to the crura cerebri and optic thalami, forming part of the diverging cere- 

 bral fibres ; each peduncle forms part of the lateral boundary of the fourth 

 ventricle, and is connected with its fellow of the opposite side by the valve of 

 Yieussens. The peduncles are continuous behind with the folia of the inferior 

 vermiform process, and with the white fibres in the interior of the corpus den- 

 tatum. Beneath the corpora quadrigemina, the innermost fibres of each peduncle 

 decussate with each other, so that some fibres from the right half of the cerebellum 

 are continued to the left half of the cerebrum. 



