FUNCTIONS OF THE BRAIN 



911 



In birds and lower vertebrates the cerebellum is only represented 

 by the worm. Yet in many of these animals the same characteristic 

 disturbances follow its removal as in the higher animals where the 

 cerebellar hemispheres have become so prominent. Indeed, it was 

 m.anly on the pigeon that Flourens made his classical experiments. 

 At first the pigeon can neither fly nor feed itself. When it attempts 

 to walk, extensor spasms of the legs come on, and it falls, wildly 

 struggling and apparently panic-stricken, to the ground. The power 

 of flight is soon regained, but for a long time the animal is unable to 

 perch, the legs and talons stiffening in rigid extension as it attempts 

 to alight. 



In the higher animals stimulation of certain parts of the worm and 

 lateral lobe causes conjugate movements of the eyes towards the same 

 side, both eyes being turned to the right e.g., when the cerebellum is 

 stimulated to the right of the middle line. Inhibition of movement 

 can also be elicited from the organ. Excitation of the cerebellar cortex 

 for some distance 

 outwards from the 

 line of junction of 

 the superior worm 

 with the lateral lobe 

 in animals which 

 exhibit tonic con- 

 traction of extensor 

 muscles after ex- 

 cision of the cere- 

 bral hemispheres 

 (decerebrate rigid- 

 ity or acerebral 

 tonus, aj it is called) 

 causes immediate 

 relaxation of the 



rigid muscles of the Fig 366 ._Scheme of Dog's Cerebellum (Dorsal View), ac- 

 cording to the Anatomical Division of Bolk (after van 

 Rynberk). La, lobus anterior, which is separated from 

 the larger posterior lobe by the deep primary fissure 

 (sulcus primarius), Spr; Ls, lobulus simplex; Si, sulcus 

 intercruralis; C 1 , crus primum; C 2 , crus secundum; 

 L.ans, lobulus ansiformis; Lp, lobulus paramedianus; 

 Lmp, lobulus medianus posterior; Fv, formatio vermi- 

 cularis (pars tonsillaris) ; Sp, sulcus paramedianus. 



neck, tail, and 

 especially the an- 

 terior limb, particu- 

 larly on the same 

 side. The relaxation 

 of the extensors 

 may be accom- 

 panied by contrac 



tion of the antago- 

 nistic flexors for example, relaxation of the triceps and contraction of 

 the biceps (Horsley and Lowenthal) . But this can scarcely be considered 

 a reaction specific to the cerebellum. For Sherrington, who finds that 

 the tonus or spasm is largely due to centripetal impulses coming from 

 the rigid limb, has been able to inhibit it by stimulation of various 

 other regions, including the portion of the cerebral cortex in front of 

 the fissure of Rolando (p. 921). 



Localization of Function in the Cerebellum. The confusion which so 

 long reigned in regard to this matter has in great measure been cleared 

 up by recent physiological work following on a more accurate anatomical 

 mapping of the lobes and lobules of the cerebellum in accordance with 

 their genetic relations (Bolk) (Fig. 366). 



Following this scheme, van Rynberk has obtained satisfactory 

 evidence of localization of function. Thus the lobulus simplex con- 

 stitutes a centre for the neck muscles, and the elimination of its influ- 



