THE CENTRAL NERVOUS SYSTEM 



831 



its cerebellum showed all the phenomena of heat or ' rut/ was 

 impregnated, whelped at full term in an entirely normal manner, 

 and manifested the maternal instincts in their full intensity. 

 Flourens put forward the doctrine that the cerebellum is an 

 organ concerned in the co-ordination of movements and 

 especially the maintenance of equilibrium, supporting his con- 

 clusions by an elaborate series of experiments. Notwith- 

 standing the very large amount of experimental and clinical 

 study which has been devoted to the cerebellum since the time 

 of Flourens, our actual knowledge of 

 its functions has not greatly ad- 

 vanced beyond the point then reached. 

 Some of the more modern authorities 

 restrict its influence entirely to the 

 actions on which equilibration de- 

 pends ; others extend it to all voli- 

 tional movements. Luciani looks 

 upon it as ' an organ which by 

 processes that do not awaken con- 

 sciousness exerts a continual strength- 

 ening (reinforcing) action upon the 

 activity of all other nerve-centres.' 

 Sherrington conceives of the cere- 

 bellum as the head ganglion of the 

 proprio-ceptive system i.e., of the 

 system of neurons whose receptors 

 lie not on the surface, but in the 

 deeper parts of the body (labyrinth 

 of ear, muscles, tendons, joints, vis- 

 cera, etc.) (p. 810). After removal of 

 the whole cerebellum (in the dog or 

 monkey), there is at first rigidity and 

 tonic spasm of certain muscles, which 

 contribute to the difficulty of co- 

 ordinating their movements. When 

 this stage has passed, the muscles all 

 over the body, but especially those of 

 the loins and hind-limbs, and those which fix the head, are 

 weaker than normal, are deficient in tone, and contract with a 

 peculiar want of steadiness (Luciani). When one lateral half 

 of the cerebellum is removed, the symptoms affect especially the 

 muscles on the same side. In extensive lesions of the cere- 

 bellum in man what has been noticed is a marked inability to 

 maintain the upright posture, giddiness, a staggering gait, 

 twitching movements of the eyes (nystagmus), tremor accom- 

 panying voluntary movements in a word, a general breakdown 



FIG. 347. CEREBELLAR COR- 

 TEX : SECTION ACROSS A 

 LAMINA (CAJAL). 



a, Purkinje's cell ; the nu- 

 merous dots in the molecular 

 layer represent cross -sections 

 of the bifurcated axons of the 

 granule cells (Golgi's method). 



