400 PHYSIOLOGY 



The roof ganglia consist of the nuclei fastigii near the middle line, the nuclei em- 

 boliformes situated just dorsal to these, and the nuclei dentati, large crenated capsules 

 of grey matter lying in the middle of each lateral lobe. The cells composing the grey 

 matter of the central nuclei are large and multipolar, resembling those found in the 

 nuclei of motor nerves. 



The cerebellum receives fibres from all the receptor apparatus of the body which 

 can be classed in the proprioceptive system. The greater number of these fibres 

 run directly to the cortex, especially of the vermis, and there is no evidence of the 

 passage of any efferent fibres from the cortex directly to the motor apparatus of the 

 cord. 



The connections of the cerebellum are established by means of its three peduncles, 

 and may be classified as follows : 



AFFERENT TRACTS. INFERIOR PEDUNCLE. By this peduncle afferent fibres 

 pass to the superior vermis: 



(1) From Clarke's column of the same side by the posterior cerebellar tract. 



(2) From the dorsal column nuclei, viz. the nucleus gracilis and nucleus cuneatus 

 of each side, so that connection is established in this way with the prolongations of the 

 posterior sensory roots which run into the posterior columns of the cord. 



(3) By the internal restiform body from the vestibular division of the eighth nerve, 

 part of the fibres passing through, and perhaps making connections with, Deiteis' 

 nucleus. 



(4) A strong band of fibres passes from the inferior olivary body into the opposite 

 cerebellar hemisphere. Atrophy of one side of the cerebellum induces a corresponding 

 atrophy in the opposite olivary body. 



MIDDLE PEDUNCLE. The broad mass of fibres making up these peduncles is partly 

 afferent and partly efferent. Many fibres originate in the ceils in the formatio reticu- 

 laris of the pons, cross the middle line, and pass up into the lateral cerebellar hemi- 

 sphere of the opposite side. Fibres also pass from the cerebellum to the pons to end 

 round cells in the same region. By this means connection is established between the 

 cerebellar hemispheres and the corticopontine fibres which pass by the crura cerebri 

 between the pons and the frontal and temporal portions of the cerebral cortex of the 

 opposite side. On account of this connection there is a close association between the 

 development of each cerebellar hemisphere and the contralateral cerebral hemisphere. 

 Atrophy of one half of the cerebrum brings about atrophy of the opposite hemisphere of 

 the cerebellum. 



THE SUPERIOR PEDUNCLE. By this path fibres from the superior corpora quadri- 

 gemima, i.e. from the terminations of the optic nerve, pass into the cortical grey matter 

 of the cerebellum (Fig. 202). 



EFFERENT TRACTS. The cerebellar cortex must be regarded as a receiving 

 rather than as a discharging station. Stimulation of it has little effect uuless strong 

 currents are employed, and a motor response is obtained more easily the deeper the 

 electrodes are sunk below the grey matter. The fibres which form the axons of the 

 cells of Purkinje pass partly towards the pons by the middle peduncle, largely, how- 

 ever, towards the roof nuclei, where they terminate. These nuclei form the efferent 

 stations of the cerebellum. From them fibres pass in various directions. A large 

 bundle leaves the dentate nucleus, runs into the superior peduncle, or braehium. 

 and passing deeply across to the tegmentum of the opposite side, traverses the red 

 nucleus to end in the subthalamic region of the opposite side of the brain. A certain 

 number of fibres, chiefly derived from the central nuclei, such as the nucleus fastigii, 

 pass forward to the corpora quadrigemina chiefly on the same side. From the ceretx^llum 

 itself no direct tract runs into the spinal cord. The nuclei of Dieters and of Bechterew 

 (the paracerebellar nuclei), which are connected with the endings of the vestibular 

 nerve, an-, however, closely associated with the roof nuclei, and give rise to descending 

 'it. iv- which pass into the antero-lateral region of the cord as the vestibule-spinal 

 tract. 



