1892.] Adductor Fibres of the Recurrent Laryngeal Nerve. 10& 



the abductor bundle ceases to produce this effect when stimulated 

 with a moderate strength of current, and when a very strong current 

 is used adduction of the vocal cord follows, as in the case of stimula- 

 tion' of the other bundle of nerve fibres. The explanation of these 

 phenomena seems to be that in the young dog the abductor fibres 

 are more excitable than the adductors, so that a strength of current 

 short of that necessary to evoke action of the adductor muscles 

 diffuses to the abductor fibres, which, being more excitable, cause 

 abduction of the vocal cord ; but that, as in the adult animal, the 

 tendency to death of the abductor fibres is more marked than that of 

 the adductors, so that there comes a time in the young animal when 

 the abductor fibres have so far lost their excitability that stimula- 

 tion of the adductor bundle with a current strong enough to evoke 

 contraction cf the adductor muscles, though it still diffuses to the 

 abductor fibres, is no longer capable of exciting them, and in the end 

 the abductor fibres lose completely their excitability, while the 

 adductors, though relatively less excitable in the beginning, preserve 

 their excitability, even in this case, longer than the abductors, which 

 on their part preserve it much longer than in the adult animal. 



Section 8. ( Control) Tracing the respective Bundles to their Peripheral 

 Terminations by Dissection. — Having ascertained by electrical excita- 

 tion the functions subserved by the different bundles of nerve fibres 

 in the nerve trunk, these bundles were traced post mortem by careful 

 dissection to their peripheral terminations. .All the bundles of nerve 

 fibres were thus dealt with, but the present research does not make 

 it necessary for a description to be given of any but the motor fibres. 

 From several such dissections, taken together with the facts ascer- 

 tained during the excitation experiments, it seemed almost certain 

 that the abductor bundle of nerve fibres is situated on the inner side 

 of the nerve, i.e., next to the trachea, while the adductor bundle is 

 situated on the outer side of the nerve. The abductor bundle may be 

 traced to the crico-arytenoideus posticus muscle on the same side, and 

 to it alone, none of the fibres to the adductors being contained in this 

 bundle ; while the adductor bundle supplies branches to all the 

 adductor muscles on the same side, and to the arytenoideus. 



Section 4. (CoyitroY) Direct Observation of the Abductor and Adductor 

 Muscles in Action after Dissection. — In six dogs the nerve was ex- 

 posed at the lower part of the neck, and the different bundles of 

 fibres separated. The nerve fibres were carefully preserved by being 

 covered with a piece of cotton wool saturated with warm normal 

 saline solution. The animal under observation was then killed by an 

 overdose of chloroform, the larynx quickly, excised, and its muscles 

 exposed by dissection. 



By this method, on excitation of the nerve fibres not only could the 

 movements of the vocal cords be seen, but also the contraction of the 



