CEEEBEAL TUMOUES. 183 



be at first limited to one limb or to parts of a limb on the 

 opposite side of the body. Jacksonian epilepsy may be associated. 

 If such a tumour happen to be at the spot where the leg centre , 

 which stands highest in the precentral convolution, adjoins the 

 trunk and arm centres which lie next below it, weakness of 

 the hip and shoulder on one side may result. (Fig. 14.) A 

 tumour in the neighbourhood of the internal capsule will 

 tend to produce hemiplegia of gradual development, and 

 so also will a tumour in the upper part of the crus com- 

 pressing the motor tract in the crusta. In the pons and 

 medulla, where the motor tracts of the two sides of the body 

 approximate, a bilateral paralysis may result, but symmetrically 

 placed tumours in the hemispheres may have the same effect. 

 (Fig. 13.) 



When a tumour is so situated as to paralyse a cranial nerve on 

 one side of the body and the limbs on the opposite side, the so- 

 called "crossed paralysis" is produced. Tumours in the crus, 

 the pons or the medulla may do this. A tumour of the crus may 

 involve the third nerve on the same side, and the rest of the 

 body on the opposite side. (Fig. 13.) 



In the upper part of the pons, the fifth nerve may be paralysed 

 on the side of the lesion, and the face, tongue, and limbs on the 

 opposite side. The facial tract crosses the mid line at the junction 

 of the upper and lower halves of the pons to reach the facial 

 nucleus, so a tumour in the lower part of the pons will completely 

 paralyse the face on the same side and involve the opposite half 

 of the tongue and opposite limbs as well, by pressing on the 

 motor tracts to these parts above their decussation. (Fig. 13.) 



A tumour on one side of the medulla, above the decussation of 

 the motor tracts in the pyramids may paralyse the tongue on 

 the same side, and the limbs on the opposite side, but this is 

 uncommon. 



The presence of certain varieties of cranial nerve paralysis is 

 important in fixing the locality of a tumour. The nucleus of the 

 third nerve extends from the back part of the floor of the third 

 ventricle to the groove between the anterior and posterior corpora 



