G02 



NERVOUS SYSTEM. 



a prominent tuft, situated behind and below the middle peduncle of the cere- 

 bellum; its surface is composed of gray matter, subdivided into a few small 

 laminae: it is sometimes called the pneumogastric lobule, from being situated 

 behind the pneumogastric nerve. The amygdala or tonsil is situated on either 

 side of the great median fissure or valley, and projects into the fourth ventricle. 

 The digastric lobe is situated on the outside of the tonsil, being connected in 

 part with the pyramid. Behind the digastric is the slender lobe, which is con- 

 nected with the back part of the pyramid and the commissura brevis: and 

 more posteriorly is the inferior posterior lobe, which also joins the commissura 

 brevis in the valley. 



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

 cerebellum, midway between its centre and the superior vermiform process, the 

 interior will be found to consist of a central stem of white matter, which con 

 tains in its interior a dentate body. From the surface of this central stem, a 

 series of plates of medullary matter are detached, which, covered with gray 

 matter, form the laminae ; and from the anterior part of each hemisphere arise 

 three large processes or peduncles, superior, middle and inferior, by which the 

 cerebellum is connected with the rest of the encephalon. 



The laminae are about ten or twelve in number, including those on both sur- 

 faces of the cerebellum, those in front being detached at aright angle, and those 

 behind at an acute angle ; as each lamina proceeds outwards, other secondary 

 laminse are detached from it, and, from these, tertiary laminae. The arrange- 

 ment thus described gives to the cut surface of the organ a foliated appearance, 

 to which the name arbor vitae 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 



Fig. 336. Vertical Section of the Cerebellum. 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 denta 'turn, or gan- 

 glion of the cerebellum, is situ- 

 ated 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 den- 

 tated outline, open at its an- 

 terior part. It is surrounded 

 by white fibres ; white fibres 

 are also contained in its in- 

 terior, which issue from it to 

 join the superior peduncles. 



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

 nect it with the rest of the encephalon. 



The superior peduncle* (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 

 cerebral fibres; each peduncle forms p:irt of the lateral boundary of the fourth 

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

 Vieussens. 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- 



