438 PHYSIOLOGY 



sides join the restiform body to pass into the middle lobe of the 



cerebellum. 



In the medulla these afferent tracts of the cerebellum are joined 

 by the following sets of fibres : 



1. The olivo-cerebellar. 



2. The vestibulo-cerebellar. 



3. A few fibres from the chief sensory nuclei, including those of the 

 vago-glossopharyngeal nerves. 



All these fibres terminate in the cortex, chiefly of the middle lobe. 

 From the cortex of this lobe fibres pass to the central and roof nuclei 

 of the cerebellum, namely, the nucleus dentatus, the nucleus emboli- 

 formis, the nucleus fastigii, and the nucleus globosus. The efferent 

 tracts of the cerebellum start from these central nuclei, no fibres 

 which originate, in the cortex of the cerebellum apparently leaving 

 the precincts of this organ. Some of these efferent fibres of the 

 cerebellum will be better described with the descending tracts of the 

 brain stem. Of those which take an ascending direction, the great 

 bulk are contained in the superior cerebellar peduncles. These 

 originate for the most part in the dentate nucleus and the nuclei 

 emboliformis and globosus. As the superior peduncles run forwards 

 they sink below the posterior corpora quadrigemina, and in the teg 

 mentum, below the Sylvian iter, decussate with the tract of the 

 opposite side to pass to the red nucleus. In the red nucleus many of 

 the fibres end, some, however,passing through the nucleus together with 

 fibres derived from the cells of the red nucleus itself to end in the 

 thalamus and in the grey matter of the subthalamic region. 



DESCENDING TRACTS 



The chief descending tracts having their origin in the brain stem 

 are the rubro-spinal bundle or bundle of Monakow, the complex 

 system of fibres known as the posterior longitudinal bundle, and the 

 vestibulo-spinal fibres from the upper part of the medulla. 



(1) The RUBRO-SPINAL FIBRES originate in the red nucleus. They 

 cross the median line and run down, at first in the tegmentum and 



later in the lateral column of the medulla oblongata and cord. In 

 their passage they communicate with the various motor nuclei of the 

 cranial nerves. They can be traced to all segments of the cord, where 

 they terminate in connection with the anterior horn- cells. 



(2) The POSTERIOR LONGITUDINAL BUNDLE. This bundle is to 

 be seen in all sections through the brain stem below the level of the 

 oculo-motor nucleus. It consists of fibres, some of which pass upwards, 

 while others pass downwards. Most of the fibres take origin in the 

 cells of Deiters' nucleus and of the reticular formation of the pons, 

 medulla, and mid-brain, as well as from certain cells in the sensory 



