146 NERVOUS SYSTEM. 



greatest interest and importance. In liemiplegia from in- 

 jury of the substance of the encephalon, particularly from 

 haemorrhage, there is almost always more or less paralysis 

 of the superficial muscles of the face. It has been observed 

 that in certain cases, the facial paralysis exists upon the 

 same side as the hemiplegia, the side opposite to the cere- 

 bral lesion, while in others, the palsy of the face is on the 

 same side as the lesion, the general hemiplegia being, as 

 usual, upon the opposite side. To explain these phenomena 

 theoretically, we must assume that in some cases, the brain- 

 lesion is to be located at a point where it involves the fila- 

 ments of origin of the facial, following them from without 

 inward, before they decussate, which would produce facial 

 paralysis on the same side as the lesion and none on the side 

 affected with general hemiplegia ; while in other cases, the 

 injury to the brain involves the roots of the facial after they 

 have decussated, when the paralysis of the face would be on 

 the same side as the paralysis of the rest of the body. It 

 would be interesting to see how far these pathological facts, 

 with their theoretical explanation, correspond with anatomi- 

 cal researches into the real origin of the nerves. 



Many anatomists have endeavored to trace the fibres of 

 the facial from their point of emergence from the encepha- 

 lon to their true origin, but with results not entirely satis- 

 factory. At the present day, it is pretty generally agreed 

 that the fibres pass inward, with one or two deviations from 

 a straight course, to the floor of the fourth ventricle, where 

 they spread out and become fan-shaped. In the floor of the 

 fourth ventricle, certain of the fibres have been thought to 

 terminate in the cells of the gray substance, and others have 

 been traced to the median line, where they decussate ; the 

 course of most of the fibres, however, has never been satis- 

 factorily established. 



It is evident, from physiological experiments, that the 

 decussation of the fibres in the floor of the fourth ventricle 

 itself is not very important. Yulpian has made, in dogs 



