808 FUNCTIONS OF THE CEREBELLUM. 



center for maintaining the equilibrium. Its connections with all of the 

 ganglionic masses of the central organs render the cerebellum adapted to 

 this purpose. 



Through the lateral cerebellar tracts stimuli are conveyed to the cerebellum 

 and these serve as guides to the position of the trunk. Connections of the vestibu- 

 lar nerve with the cerebellum have a similar effect with respect to the equilibrium. 

 The cerebellum may influence the motor nerves of the spinal cord through fibers 

 that pass downward through the restiform body into the lateral tract of the 

 spinal cord. The cerebellum itself is insensitive to injuries. 



The experiments of Luciani upon the functions of the cerebellum 

 prove that each portion of this structure has the same function as the 

 whole. The functions are threefold : i. The cerebellum provides volun- 

 tary movements with sufficient strength. 2. It increases the tone of the 

 muscles during rest. 3. It accelerates the rhythm of the individual 

 motor impulses that constitute the movements and it fuses the impulses 

 into a continuous act. 4. Russell has found, after extirpation of the 

 cerebellum, incoordination of movement, rigidity of the muscles, and 

 motor weakness as characteristic symptoms. 



After almost complete removal of the cerebellum dogs exhibit paresis and 

 deficient tone especially in the muscles of the vertebral column and the hind legs. 

 The animal is able neither to stand nor to walk and the head oscillates to and fro. 

 Immediately after the operation there appear as irritative phenomena: tonic 

 spasm of the muscles of the nape of the neck, the back, and the forelegs, con- 

 vergence of the eyes, occasionally falling forward of the body. Intelligence and 

 sense-impressions, including the muscle-sense, remain intact. 



Median division of the cerebellum without extirpation causes permanent 

 enfeeblement of all voluntary movements, diminution of the muscular tone present 

 during rest, as well as tremor, discontinuous muscular contractions, incoordination 

 and uncertainty in voluntary movements. Extirpation of the vermis causes, as 

 irritative phenomena, tonic contraction of the muscles of the nape of the neck 

 and of the forelegs, which at times is followed by paresis especially of the hind 

 legs. Complete removal of one-half of the cerebellum is followed, as irritative 

 phenomena, by rolling movements about the longitudinal axis, as well as rotation 

 of the eyes toward the unaffected side, curvature of the vertebral column toward 

 the side operated on and tonic extensor spasm of the foreleg and less commonly 

 of the hind leg upon the same side. These are followed, as paralytic phenomena, 

 by relaxation of the muscles of the same side (atony), a somewhat less energetic 

 contraction (asthenia) and a want of fusion of the composite movements, so that 

 tremor, swaying and rhythmic oscillations (astasia) result. Superficial injury or 

 partial removal of one hemisphere is neutralized by the assumption of its function 

 by the intact portions of the cerebellum. Animals deprived of their equilibrium 

 after extirpation of the cerebellum can regain it through the motor impulses 

 gradually sent from the motor cortical centers of the cerebrum in standing, walk- 

 ing, and swimming. 



Luciani observed, eventually, in animals after extirpation of the cerebellum, 

 general marasmus, and he believed, therefore, that the organ exercises a trophic 

 function. In accordance with this view, Friedeberg observed loss of weight after 

 disease of the cerebellum. 



Extirpation of the cerebellum is followed by secondary degeneration of the 

 portion of the pons surrounding the pyramids, of the inferior olivary bodies, all 

 of the cerebellar peduncles and the direct cerebellar bundle of Flechsig, principally 

 on the same side, in lesser degree on the opposite side. Degeneration takes place, 

 also, in some fibers within all of the cerebral nerves and the anterior roots of the 

 spinal nerves. 



In frogs an important organ for locomotion is situated at the junction of the 

 medulla with the cerebellum. After its removal the animal is no longer able to 

 hop about or to creep in a coordinate manner. 



Pathological. Asymmetrical or unilateral lesions of the cerebellum cause in 

 man a tendency to fall toward the side of the injury, while bilateral injuries cause 

 a tendency to fall backward. If the middle lobe is affected disorders of coordi- 

 nation occur, particularly a stumbling, staggering gait and marked vertigo, as 



