THE CENTRAL NERVOUS SYSTEM. 71 



THE FUNCTIONS OF THE PONS. 



The nucleus of the sixth nerve and the motor nuclei of the fifth and 

 seventh nerves receive efferent fibres from the cortex of the cerebral 

 hemisphere, which have descended in the pyramid and crossed the 

 middle line in the pons itself. Hence a unilateral lesion in the pons 

 may be characterised by paralysis of the external rectus muscle of the 

 eye and of the muscles of the face on the side of the lesion, along with 

 paralysis of the arm and leg on the side opposite to the lesion. 



The pons also forms the crossing place for the path, described above, 

 of the fibres which connect one cerebral hemisphere with the cerebellar 

 hemisphere of the opposite side. 



The motor paths and the rubro-spinal tract pass through the pons, 

 the former giving off fibres to the pontine motor nuclei in the manner 

 already described. 



The ascending tracts already described in connection with the 

 medulla oblongata, with the exception of those which form the restiform 

 body, pass through the pons unchanged. The fillet receives in its 

 course additional fibres from the nuclei of the cochlear and fifth nerves. 



The chief vestibular nucleus and the nucleus of Deiters are concerned 

 with the function of equilibration. The axons of these nuclei divide into 

 two groups, one group passing to the cerebellum in the restiform body, 

 the other joining the posterior longitudinal bundle which links the 

 oculo-motor and vestibular nuclei with the spinal cord. 



SECTION VI. 

 THE CEREBELLUM. 



The cerebellum is connected with the medulla oblongata and with 

 the vestibular nuclei of the pons by the restiform body or inferior 

 cerebellar peduncle on each side, with the pons by the two brachia 

 pontis or middle cerebellar peduncles, and with the mid-brain by the 

 two brachia conjunctiva or superior cerebellar peduncles. It consists 

 of a middle lobe or vermis and two lateral lobes. The surface of the 

 cerebellum is thrown into numerous folds, and the superficial layer, 

 consisting of grey matter, is thus much increased in extent. The 

 interior of the cerebellum is mainly composed of white matter, 

 but it also contains some masses of grey matter, known as the 

 nucleus dentatus, nucleus emboliformis, nucleus globosus, and nucleus 

 fastigii. 



The cortical substance consists of two layers with a single row of 

 large nerve cells lying between them (fig. 20). These large cells are 



