112 Fibres of the Recurrent Laryngeal Nerve. [Mar. 31, 



fibres in the nerve trunk that excitation of either of them evokes con- 

 traction of the abductor or adductor muscles, as the case may be, 

 without evoking any contraction whatever in the muscle or muscles 

 of opposite function. 



8. That the bundle of nerve fibres concerned with one function 

 may be divided without injury to that concerned with the opposite 

 function, and that such division is followed by atrophy and degenera- 

 tion of the muscles related to that function without any such changes 

 being detectable in the muscles related to the opposite function. 



Further, it was clear that the theory advanced by Mackenzie, and 

 which has since found favour with many, viz., that possibly the reason 

 why the abductor fibres succumb before the adductor in affections of 

 the nerve is because they are more superficially and circumferentially 

 arranged, while the adductor fibres are situated deep in the sab- 

 stance of the nerve, is shown by these experiments to be entirely 

 erroneous. 



One point which is difficult to explain is why there should be so 

 marked a difference between the recurrent laryngeal nerve of a young 

 and that of an adult dog, as regards the respective predominance ot: 

 abductor or adductor representation in the trunk of the nerve. 

 Possibly the reason why the abductor influence is in the ascendency 

 in the young dog is because the power of phonation is still imper- 

 fectly developed, and with it both the muscle and nerve fibres sub- 

 serving this function are also imperfectly developed, while the 

 function of respiration is from the beginning fully developed, and 

 with it the muscle and nerve fibres connected with that function. 

 That the reverse should be the case in the adult animal may well be 

 due to the fact that phonation is perfectly developed, while respira- 

 tion has become so automatic that very feeble stimuli are necessary to 

 keep it going. 



My sincere thanks are due to Professor Victor Horsley for allowing 

 me to carry out this research in the Pathological Laboratory of 

 University College, London, and for being so good as to verify the 

 results which I obtained from time to time. 



I wish also to express my thanks to Dr. Felix Semon for having 

 very kindly given me access to his valuable collection of literature on 

 the subject, and facilitating the work of writing this paper. 



