THE CEREBELLUM. 245 



h. Secondary visceral sensory fibers. These are the fibers 

 of the direct cerebellar tract from Clarke's column in the cord. 

 Most authors state that this tract ends in the deep gray nuclei 

 but it is sometimes described as ending in the cortex of the vermis. 



The fibers which go out from the cerebellum are all neurites 

 of Purkinje cells. They go to the spinal cord, the lower oHve, 

 Deiter's nucleus, nuclei of the pons and perhaps to other centers. 

 By way of these various paths the cerebellum may exercise control 

 over both somatic and visceral motor nerves. A part of the fibers 

 which go through the middle peduncle to the pons go directly 

 to the spinal cord to connect with the somatic motor column. 

 Other fibers end in the nuclei of the pons, from which fibers go 

 to the opposite cerebellar cortex or to the cerebral cortex. Many 

 Purkinje cell neurites may end in the nucleus dentatus, from 

 which the large brachium conjunctivum goes to the optic thai- 

 ami. By this path and the tractus thalamo-spinalis the cerebel- 

 lum may gain a widespread connection with motor nerves. 



There is no one fact more striking in the study of the human 

 brain than the great complexity of structure and fiber connections 

 of the cerebellar cortex and the great increase in the number of 

 relationships of the cerebellum from lower to higher vertebrates. 

 Much remains to be done, especially on the course of Purkinje 

 cell neurites, in order to gain an exact knowledge of these rela- 

 tionships. 



Nucleus dentatus. — The nucleus dentatus is taken up sepa- 

 rately from the other deep gray masses because of its apparent 

 closer relation with the cortex. The peculiar form of the nucleus 

 which gives it its name in man is not seen in lower mammals. 

 In these it is a simple gray body which lies nearer to the surface 

 of the brain and nearer the junction of the cerebellum with the 

 medulla oblongata. The fibers which enter the nucleus dentatus 

 are not fully understood but they seem to include external arcuate 

 fibers from the nuclei of the dorsal funiculi, fibers from some 

 of the nuclei of the vestibular nerve and fibers of Purkinje cells 

 of the cortex. The neurites arising in the nucleus dentatus go 

 mostly or wholly into the brachium conjunctivum which is com- 

 posed almost exclusively of such fibers (Van Gehuchten). The 



