MESENCEPHALIC ROOT 175 



results, while decidedly more extensive, confirm in the main the 

 chromatolytic studies of May and Horsley. 



A year later Kosaka approached this problem from the 

 standpoint of chromatolysis. He experimented mamly on dogs, 

 but made use of rabbits and monkeys. His method of pro- 

 cedure was to tear out one of the trigemmal nerve branches or 

 "muscles innervated by one of these nerves and count the number 

 of degenerated cells in the mesencephalic root nucleus on the 

 operated side. The author found if the third division of the 

 trigeminal (N. mandibularis) was destroyed in the rabbit, dog, 

 and monkey that he obtained a complete chromatolysis of 

 nearly all of the cells of the mesencephalic root nucleus on the 

 side of the operation, while no chromatolysis resulted from 

 injury to the first division of the trigeminus (N. ophthalmicus). 

 Upon severing the second division of the trigemmus (N. maxil- 

 laris) in the dog and monkey, he found a few degenerated cells 

 in the mesencephalic root nucleus, the number varying according 

 to the region of the lesion. In four experiments on dogs 12 

 to 59 disintegrated cells were found in a nucleus comprised of 

 1116 to 2427 cells and in a monkey 71 disintegrated cells ap- 

 peared in a nucleus comprised of 2744 cells. No chi'omatolysis 

 in the rabbit as a result of cutting the N. maxillaris. Further- 

 more, Kosaka reports that a lesion of almost any branch, sensory 

 or motor, of the N. mandibularis brought about a degeneration 

 of some of the cells of the mesencephalic root nucleus on the 

 side of the injury. For example, in the N. hngualis 7 cells 

 underwent- chromatolytic changes and in the case of the digastric 

 nerve 7 cells disintegrated. When the M. tensor veli palatini 

 were removed from one side 22 cells degenerated, in the case of 

 the M. temporalis, 30, and in the M. masseter, 20. It will be 

 seen in connection with the last two nerves that Kosaka found 

 considerably less chromatolysis in the mesencephalic nucleus 

 than Willems and less than one would expect to be present. 



Kosaka concluded that the mesencephalic root cells are con- 

 cerned with both muscle and cutaneous sensations, and that 

 they are more or less localized in the midbrain, the muscle sense 

 cells being situated below the trochlear nucleus. He agrees with 



