FORCED MOVEMENTS NYSTAGMUS. 721 



may be paralysis of the oculomotorii on both sides. Disease of the posterior pair may be 

 associated with disturbances of co-ordination (Nothnagel). 



Forced Movements. It is evident from what has been said regarding the 

 importance of the corpora quadrigemina for the harmonious execution of movements, 

 that unilateral injury of such parts as are connected with them by conducting 

 channels, must give rise to peculiar unilateral disturbance of the equilibrium, 

 causing variations from the symmetrical movements of both sides of the body. 

 These movements are called forced movements. To this class belong the " mouve- 

 ments de manege," where the animal, instead of moving in a straight line, runs round 

 in a circle; index movements, where the anterior part of the body is moved 

 round the posterior part, which remains in its place, just like the movements of an 

 index round its axis ; and rolling movements, when the animal rolls on its long axis. 

 All these forms of movement may pass into each other, and they are, in fact, merely 

 different varieties of the same kind of movement. The parts of the nervous system 

 whose injury produces these movements are the corpus striatum, optic thalamus, 

 cerebral peduncle, pons, middle cerebellar peduncles, and certain parts of the 

 medulla oblongata. Eulenburg observed index movements in the rabbit, after 

 injury to the surface of the brain, and Bechterew observed the same in dogs. 

 Forced movements, together with nystagmus and rotation of the eyeballs, are 

 caused by injury to the olives (Bechterew). The statements of observers vary as to 

 the direction and kind of movement produced by injuring individual parts. The 

 following observations have been made : Section of the anterior part of the pons, 

 and of the crura cerebelli causes index, or, it may be, rolling movements towards 

 the other side; section of* the posterior part of the same regions causes rolling move 

 ments towards the same side, while the same result is caused by a deeper puncture 

 into the tuberculum acusticum, or into the restiform body. Section of one cerebral 

 peduncle causes mouvements de manege, while the body is curved with the con- 

 vexity towards the same side. The nearer to the pons the section is made, the 

 smaller is the circle described ; ultimately index movements occur. Injury to one 

 optic thalamus produces results similar to puncture of the anterior part of the 

 cerebral peduncle, because the latter is injured along with it at the same time. 

 Injury to the anterior part of one optic thalamus causes the opposite kind of forced 

 movement, viz., with the concavity of the body towards the injured side. Injury 

 to the spinal portion of the medulla oblongata is followed by bending of the head 

 and vertebral column, with the convexity towards the injured side, along with 

 movements in a circle. When the anterior end of the calamus and the part above 

 it are injured, the movements are towards the sound side. 



Strabismus and Nystagmus. Amongst the forced movements may be reckoned 

 deviation of the eyeballs, strabismus or squinting, and involuntary oscillation of the 

 eyeballs, constituting nystagmus. The latter condition occurs after superficial 

 lesions of the restiform body, as well as of the floor of the 4th ventricle. A 

 unilateral, deep, transverse injury, from the apex of the calamus upwards as far as 

 the tuberculum acusticum, causes the eye of the same side to squint downwards 

 and forwards, that of the other side backwards and upwards. Section of both sides 

 causes this condition to disappear (Schwahn). Hence, Eckhard assumes that the 

 medulla oblongata is the seat of an apparatus controlling the movements of the 

 eyes (Eckhard), which can be excited by sudden anaemia, e.g., ligature of the 

 cephalic arteries in a rabbit. 



In pathological degeneration of the olivary body of the medulla oblongata in man, Meschede 

 observed intense rotatory movements towards the same side. 



Theory. In order to explain the occurrence of forced movements, it is suggested that there 

 is unilateral incomplete paralysis {Lafarque), so that the animal in its efforts to move onward." 

 leaves the paralytic side slightly behind the other, and hence there is a variation from the 

 symmetry of the movements. Brown-Sequard regards the matter in exactly an opposite light, 

 viz., as due to stimulation from injury, causing an excessive activity of one-half of the body. 



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