_Ataxia and inco-ordination of movement_ are also prominent symptoms. Ataxia results from one or more of the following causes: (1) co-existent vertigo, (2) asthenia of the muscles of the affected side, the muscular contractions being irregular in their nature, ill-timed in their action, and often in excess of actual requirements, and (3) involvement of the spino-cerebellar tracts and their terminations. The patient, when standing with the eyes shut and one foot advanced in front of the other, is unable to maintain his balance, staggers and tends to fall. No great diagnostic value can be attached to the direction in which he sways or falls, though, from my own experience, it would appear more probable that he should lurch towards that side on which the tumour is situated. In walking, however, there is occasionally a definite tendency to deviate towards the opposite side, probably due to over-correction of the weakened muscles on the affected side. The gait should present the typical appearance of cerebellar ataxia, and the patient may walk with the head drawn down towards the shoulder of the affected side, the chin being tilted in the opposite direction. Inco-ordination of movement is rendered most obvious during active movement of the limb, decreasing towards the termination of that movement, and ceasing so soon as the object is attained. This is most readily demonstrated by the well-known ‘finger-to-nose’ test. _Nystagmus_ is one of the most frequent symptoms of cerebellar tumour, usually lateral, the movements coarse or fine, and most marked when the eyes are directed towards the side of the lesion. In the more differential diagnosis between _extra- and intra-cerebellar_ tumours, the following points should be noted:-- _Extra-cerebellar_ tumours situated in the cerebello-pontine angle tend to lead to compression of the eighth nerve (with deafness and tinnitus), of the seventh nerve (with paralysis of the face muscles), of the fifth nerve (with anæsthesia of the parts supplied by that nerve), and more rarely of the sixth nerve (with paralysis of the external rectus). The ninth, tenth, eleventh, and twelfth nerves are but rarely involved. _Intra-cerebellar_ tumours seldom give rise to pressure effects on isolated cranial nerves. On the other hand, one expects ipso-lateral paresis or paralysis, with exaggerated reflexes (see Fig. 78). Conjugate deviation of the eyes to the side opposite to that on which the tumour is placed is a fairly frequent symptom, the deviation being associated with well-marked lateral nystagmus. When the tumour is of considerable size, or placed nearer the central portion of the cerebellum, pressure may be exerted on the pyramidal fibres with paresis or paralysis on the contra-lateral side of the body.