FUNCTIONS OF THE BKAIN. 827 



supposed that the direct cerebellar paths of the cord conduct sensoiy 

 impressions to the cerebellum, and thus indicate the posture of the 

 trunk and the position of the limbs, while the motor impulses passing 

 through the cord may be influenced by fibres passing from the 

 cerebellum through the restiform body to the lateral columns. Injuries 

 of the cerebellum produce no disturbance of the psychical function, nor 

 do they give rise to pain. When, however, the cerebellum is gradually 

 removed, as in a pigeon, at first symptoms of weakness and slight 

 disturbance of movement are evident ; as more and more of the 

 cerebellum is removed great excitement appears, and the animal now 

 makes violent irregular movements, which, while not similar to convul- 

 sions, are yet free from all apparent purpose; while co-ordinated 

 movements are impossible vision and hearing, nevertheless, remain 

 intact. 



Again, section of the middle cerebellar peduncle on one side almost 

 always gives rise to forced movements, the animal revolving rapidly on 

 its own longitudinal axis, and this disturbance is accompanied by 

 nystagmus, or oscillation of the eyeballs. 



Injury or removal of the lateral lobe produces the same forced 

 movement as section of the middle peduncle. 



In mammals the dangers are so great in operations on the 

 cerebellum that but few successes are on record. In operations of 

 extirpation performed on mammals which have proved successful, at 

 first the symptoms are those of irritation of the divided peduncles, and 

 consist in clonic contractions of the muscles of the fore limb, neck, and 

 back, while no sensory disturbances are perceptible. When recovery 

 from the operation is complete the symptoms dependent upon the 

 loss of the cerebellum then appear and consist mainly in disturbances 

 of equilibrium, and, while many muscular groups apparently maintain 

 their muscular tone intact, the power of associating various groups of 

 muscles to produce complex actions is lost. When the injurj^ to or 

 extirpation of the cerebellum has been but superficial the disturbances of 

 co-ordination soon pass off, while if the injury affects the lowest third 

 of the cerebellum the effects are permanent. 



We may now return to the subject of the conduction of motor and 

 sensory impulses through the central nervous 53' stem, summarizing the 

 statements which have been made during the consideration of the func- 

 tions of the spinal cord, medulla oblongata, and brain (Fig, 359). 



Sensory impulses originating in stimulation of the peripheral termi- 

 nations of afferent or sensory nerves pass into the cord through the 

 posterior roots of the spinal nerves, and the impulse passes either to the 

 cerebrum or cerebellum or both. After entering the cord the fibres of 

 the posterior roots diverge and carry the afferent impulses in different 



