158 



Scientific Proceedings (76). 



4. Unilateral removal of the labyrinth and section of 



the dorsal roots of the cervical nerves 

 on the same side. 

 When these procedures are successively applied to the same 

 side, the degree of head torsion brought on by the first procedure 

 is always accentuated upon application of the second. As in the 

 experiments of the series 2, the order of the experiment can be 

 reversed without influencing the results. 



5. Unilateral removal of the labyrinth and section of 

 the dorsal roots of the cervical nerves on the same 



side, followed by either (a) removal of the re- 

 maining labyrinth, or (b) section of the re- 

 maining dorsal cervical roots. 



In this series the accentuated torsion appearing after the second 

 procedure is decreased on applying the third. 



These results indicate that the torsion of the head resulting 

 from destruction of the labyrinth is caused by an impairment of 

 tonus in the neck muscles on the side of the lesion. The cervical 

 musculature involved in torsion of the head is influenced by two 

 distinct tonus mechanisms. The afferent impulses of the first 

 mechanism arise in the otic labyrinth; those of the second arise 

 in the peripheral endings of the fibers of the dorsal roots of the 

 cervical nerves. Injury to either of these two mechanisms does 

 not result in absolute loss of tonus in the cervical musculature, for 

 when destruction of the labyrinth and section of the dorsal roots 

 of the cervical nerves are combined on the same side, the degree of 

 head torsion brought by the first lesion is somewhat accentuated 

 by the second. 



The relation of possible cerebellar paths to the labyrinthine 

 head torsion is now under investigation. The data available at 

 present are outlined below. 



6. Unilateral removal of the labyrinth and section of 



the inferior cerebellar peduncle on either side. 

 The torsion resulting from destruction of the labyrinth is not 

 modified to any considerable extent by section of the posterior 

 cerebellar peduncles. 



