FORCED MOVEMENTS. 807 



index-movement and rolling movements toward the opposite (paretic?) side; section 

 of the posterior portion of the same regions causes rolling movements toward the 

 same (paretic?) side, as does also deeper puncture of the auditory tubercle or the 

 restiform body. Incision of one cerebral peduncle causes circular movement, 

 with the convexity directed toward the same side. The closer the incision is 

 situated to the pons the narrower becomes the circle of movement. Finally, 

 index-movement occurs. Injury of one optic thalamus causes much the same 

 phenomena as puncture of the anterior portion of the cerebral peduncle, because the 

 latter is injured at the same time. Injury of the anterior portion of one optic 

 thalamus gives rise to forced movement in the opposite direction, that is with the 

 concavity directed toward the side of the injury. Flexion of head and vertebral 

 column, with the convexity toward the affected side, together with circular move- 

 ment, is caused by injury of the spinal extremity of the medulla; the convexit}^ is 

 directed toward the unaffected side as a result of injury to the anterior extremity 

 of the calamus and above. 



Rotation (strabismus) and involuntary oscillation (nystagmus) of the eyes 

 may be included among forced movements. Nystagmus occurs as a result of 

 unilateral superficial lesions of the restiform body, as well as of the floor of the 

 fourth ventricle, and as a result of irritation of the cerebellum. Unilateral, deep, 

 transverse injuries from the apex of the calamus downward to the auditory 

 tubercle cause strabismus of the eye of the same side downward and forward, 

 and of the opposite eye backward and upward. Bilateral injuries cause this 

 strabismus to disappear. It is, therefore, to be inferred that the medulla ob- 

 longata contains a mechanism controlling the ocular movements, which can 

 be irritated as a result of sudden anemia (ligature of the cerebral arteries in the 

 rabbit) . 



In explanation of the forced movements it has been in part assumed that they 

 are due to unilateral incomplete paralysis, so that the animal, on attempting to 

 move about, drags the paretic side somewhat (as, for example, in the circular 

 movement on the side of the body directed toward the center of the circle) , and 

 therefore the symmetry of movement is lost. Others have attempted, in direct 

 opposition to this view, to establish an irritation through the act of injury as the 

 cause of an excessive activity upon one side of the body. Landois, as a result 

 of his own observations, ranged himself on the side of those investigators who 

 consider vertiginous sensations induced by the injury as the cause of the move- 

 ments. He observed, at times, that immediately after the injury (stilet-puncture) , 

 the movement took place in a direction opposite to that appearing somewhat 

 later. He considered this phenomenon as the effect of the irritation and paraly- 

 sis induced in quick succession by the injury. The latter, by irritating or paralyzing 

 the apparatus controlling locomotor sensations, may give rise to a false impression 

 as if the body of the animal or also the objects of the external world moved in 

 a definite direction. As a result of this motor deception the movements described 

 are executed as a reaction, with the intention of correcting the abnormal fictitious 

 movements by means of suitable counter-movements. The circular movements 

 after injury of the optic thalamus may be induced by apparent movement in 

 consequence of injury to the optic nerve. 



In this connection it may be mentioned that injury of a point not far from 

 the posterior extremity of the cerebral hemisphere causes after the lapse of some 

 time marked forward or lateral movements, likewise probably as the result of a 

 false motor impression. The unrestrained running movement after injury of an 

 area in the middle of the striate body near the free margin directed toward the 

 ventricle is probably to be explained in the same way. At first the animal re- 

 mains quiet. If driven, however, it runs furiously until restrained by some ob- 

 struction. Landois has made the observation that every manipulation of the 

 central organs that affects the equilibrium in considerable degree is attended 

 with marked increase and deepening of the respirations. 



FUNCTIONS OF THE CEREBELLUM. 



Injuries of the cerebellum cause in marked degree disturbances in 

 the harmony of the movements of the body. Probably the cerebellum 

 represents a central organ for the more delicate gradation and the nor- 

 mal sequence of movements, inasmuch as it regulates especially con- 

 tinuous and tonic muscular contractions. Thomas designates it a reflex 



