462 THE INTERNAL STRUCTURE 



monly believed to pass under the posterior extremity of 

 the Thalamus, and from this body to different regions of 

 the Cerebral Cortex — though they have not been actually 

 traced further than into different parts of the ' corona 

 radiata.' 



Nothing, therefore, is known as to the particular Con- 

 volutions with which the Cerebellum is brought into 

 relation through these fibres of the Upper Cerebellar 

 Peduncles. On the Cerebellar side, however, these par- 

 ticular fibres are thought to be partly in immediate 

 relation with the cortex of the inferior portions of the 

 Middle Lobes (fig. 165) ; wdiilst others of them, on each 

 side, are in communication with, or enter the bag-like 

 grey nucleus (fig. 156) before passing to different portions 

 of the Cerebellar Cortex. 



Between these converging Upper Peduncles there is a 

 thin lamina of nerve matter known as the * valve of 

 Vieussens ' that suffices to connect the Middle Lobe of 

 the Cerebellum with the Corpora Quadrigemina. This is 

 a structure which in lower Vertebrates, such as Fishes, 

 is proportionately more developed, and serves to bring their 

 large ' optic lobes ' into structural connection with the 

 only portion of the Cerebellum that they possess, viz., 

 the Middle Lobe. This lamina forms the roof of the 

 upper or anterior half of the ' fourth ventricle ' (fig. 152) 

 and also of the first part of the passage between this 

 cavity and the * third ventricle.* 



The Lower Peduncles, or ' restiform bodies ' as they 

 are also termed, connect the Cerebellum with the Medulla 

 and Spinal Cord (fig. 165). Within the Cerebellum the 

 fibres of these Peduncles are said not to come into relation 

 with the central bag-like grey nuclei, but to pass at once 

 to different regions of the cortical grey matter. 



The inner portion of each Lower Peduncle appears to 



