836 A MANUAL OF PHYSIOLOGY 



disturbances follow its removal as in the higher animals where the 

 cerebellar hemispheres have become so prominent. Indeed, it was 

 mainly 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 contraction of extensor muscles after excision 

 of the cerebral hemispheres (decerebrate rigidity or acerebral tonus, 

 as it is called) causes immediate relaxation of the rigid muscles of 

 the neck, tail, and especially 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 reaction specific to the cere- 

 bellum. 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. 847). 



Forced Movements. We have incidentally mentioned that in 

 fishes injuries to the semicircular canals may give rise to movements 

 which seem to be beyond the control of the animal, and which have 

 consequently received the name of ' forced movements.' It may be 

 added that when the internal ear of a Necturus (one of the tailed 

 amphibia) is destroyed on one side, rapid movements of rotation 

 around a longitudinal axis are observed. The animal spins round 

 and round apparently without voluntary control, purpose, or 

 fatigue. The direction of rotation is towards the side of the lesion, 

 the observer being supposed to look down upon the animal as it lies 

 in its normal position. After a time it becomes quiescent ; but the 

 forced movements can be again produced by pinching or exciting it 

 in other ways.* In man, too, during the passage of a galvanic current 

 through the head by electrodes applied just behind the ears, a 

 tendency to move the head towards the anode is experienced. The 

 person may resist the tendency, but if the current be strong enough 

 his resistance will be overcome ; he will execute a forced movement. 

 When the head turns towards the anode the eyes move in the same 

 direction, and then undergo jerking movements towards the kathode. 

 There is at the same time a feeling of vertigo. Complex as such an 

 experiment is, involving as it does stimulation of so many structures 

 within the cranium, there is reason to believe that it is the excitation 

 of the semicircular canals, or their cerebellar connections, that is 

 responsible for these forced movements. For when the experiment 

 is performed on a pigeon, forced movements are caused so long as 

 the membranous canals are intact, but not after they have been 

 * Personal observation. 



