THE STRUCTURE OF THE BRAIN STEM 387 



thalamus. the former in special relation with the organ of vision, the latter 

 with the organ of hearing. 



The olfactory bulb is also connected by tracts with the thalamic region, 

 probably through the column of the fornix and the bundle of Vicq d'Azyr. 

 Since however the chief connections of the olfactory lobe are with the 

 more primitive portions of the cerebral hemispheres, the olfactory tracts 

 will be more conveniently treated -of in connection with the latter. 



THE CEREBELLAR PATHS. We have already traced out the course of 

 spinal fibres which terminate in the cerebellum. They may be shortly 

 summarised as follow > : 



(1) The posterior or direct cerebellar tract, originating in Clarke's 

 column of cells of same side, passing up in the lateral columns and by 

 the restiform body into the superior vermis of the middle lobe of the 

 cerebellum. 



(2) The anterior cerebellar tract or tract of Gowers, originating in the grey 

 matter of both sides of the cord and passing in the lateral columns through 

 the lateral part of the medulla and pons, and finally attaining the superior 

 vermis through the superior cerebellar peduncles. 



(3) The posterior columns, ending chiefly in the homolateral posterior 

 column nuclei. From these nuclei, though the great mass of fibres passes 

 into the fillet, a certain number from the nuclei of both sides join the resti- 

 form 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. 



_. The vestibulo-cerebellar. 



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

 -In < >pharyngeal 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 cere- 

 bellum, namely, the nucleus dentatus. the nucleus emboliformis, 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 origin- 

 ate for the most part in the dentate nucleus and the nuclei emboliformis and 

 globosus. As the superior peduncles run forwards they sink below the 

 p"M:erior corpora quadrigemina. and in the tegmentum, below the Sylvian 

 iter. decussate with the tract of the opposite side to pass to the red nucleus. 

 Li 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. 



