942 



THE CENTRAL NERVOUS SYSTEM 



L.ana 



\ 



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 

 l me f 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, as it is called) 

 causes immediate 

 relaxation of the 

 rigid muscles of the 

 neck, tail, and espe- 

 cially the anterior 

 limb, particularly 

 on the same side. 

 The relaxation of 

 the extensors may 

 be accompanied by 

 contraction of the 

 antagonistic flexors 



for example, relaxation of the triceps and contraction of the biceps 

 (Horsley and Lowenthal). But this can scarcely be considered a re- 

 action 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. 955). 



The confusion which so long reigned in regard to cerebellar 

 localization has in great measure been cleared up by recent physio- 

 logical work following on a more accurate anatomical mapping of the 

 lobes and lobules of the cerebellum in accordance with their genetic 

 relations (Elliott Smith, Bolk) (Figs. 378, 379). The classical descrip- 

 tion of the mammalian cerebellum as consisting of a median lobe or 

 vermis and two hemispheres has been abandoned by the modern 

 investigators in this field. They divide the organ into two chief 

 lobes, an anterior and a posterior, separated by the deep and constant 

 primary fissure. 



Fig. 378. 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 , cms primum; C 2 , cms secundum; 

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

 Lmp, lobulus medianus posterior; Fv, formatio venni- 

 cularis (pars tonsillaris); Sp, sulcus paramedianus. 



