THE NERVOUS SYSTEM 481 



the brain. The incoming fibres sweep through the peduncles 

 and terminate in the grey matter in the manner already de- 

 scribed. The efferent fibres originating in the cells of Purkinje 

 do not pass out through the peduncles directly as fibres derived 

 from the cortex ; these cortical fibres first terminate in nuclei, 

 and from the cells of the nuclei fresh fibres are formed. 



Through the anterior peduncle fibres pass from the cells of 

 Purkinje to the mid-brain. This is the only purely efferent tract 

 assigned to the cerebellum, and the distribution of the fibres is 

 peculiar and complex. The peduncles converge and meet in the 

 mid-brain ; by so doing their fibres decussate, so that impulses 

 from the cerebellum pass to the opposite side of the brain, where 

 they are conveyed to the red nucleus. This is the second cell 

 station for the efferent fibres. In the red nucleus, part of the 

 fibres are sent upwards to the cerebral cortex by means of fibres 

 known as thalamo- cortical, and part pass backwards by a special 

 tract known as the bundle of Monakow, or rubrospinal tract, 

 which in its passage to the medulla crosses the central line, so 

 that impulses pass down the lateral columns of the cord on the 

 same side as they issue from the cerebellum. In this way, 

 broken as it is, the cerebellum is brought into communication 

 with its own side of the cord, which is in contrast with the con- 

 nection existing between the cerebrum and spinal cord, which is 

 crossed. By means of the anterior peduncle the fibres of the 

 ventro-lateral ascending tract of the cord (tract of Gowers) also 

 gain entrance to the cerebellum, being distributed to the lower 

 part of the vermis. 



By means of the middle peduncle the cerebellum is brought 

 into communication with the pons, while from nuclei in the pons 

 fibres pass to the cerebrum. This is the second indirect path 

 between the cerebrum and cerebellum, but in this case it is 

 afferent — viz., the communication is from cerebrum to cere- 

 bellum. 



Through the posterior peduncle, which is formed by the resti- 

 form body of the medulla, another important afferent path is 

 opened up to the cerebellum, but in this case from the spinal cord. 

 The direct cerebellar tract passes unbroken through the bulb, 

 through the posterior peduncle, its fibres being mainly distributed 

 to the vermis on the same side. Other very important fibres are 

 conveyed by this peduncle from the eighth pair of cranial nerves, 

 constituting a connection between the cerebellum and the 

 labyrinth. The eighth pair of nerves arises from two roots ; one 

 from the vestibule of the ear is in no way connected with the 

 sense of hearing, but is entirely devoted to the question of body 

 equilibrium and allied matters. This branch gains access to 

 the cerebellum through the posterior peduncle. It will be ob- 



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