R E S I' I R A T [ON I N T II E C II E L U N 1 A 29 



our most careful and complete study. So novel and surprising wen- some of its 

 results that avc have felt ii right to surround ourselves with more than common 

 precautions. For this purpose we have repeated our experiments and dissections 

 on several species of turtles, and on numerous individuals of each species, until 

 incessant repetition left no question unanswered, and no conclusion doubtful. 



We shall study, 



1st. The physiology of the pneumogastric nerve and its branches, so far as they 

 concern the respiratory function. 



2d. The physiology of the nerves which supply the respiratory muscles of the 

 breast-box. For all necessary details as to the anatomy of the vagus nerve and its 

 branches Ave refer to the former part of this memoir. Here it will only be requisite 

 to repeat that, as in most mammals, the larynx receives a superior laryngeal nerve, 

 and an inferior or recurrent laryngeal trunk. The superior, which in man is 

 the nerve of sensation to the larynx, is in turtles distributed to the mucous 

 membrane of that organ, and also to both of the glottic muscles. The recur- 

 rent laryngeal, which in man is the principal motor nerve to the larynx and 

 glottis, is in turtles also motor, but it sends branches only to the opening muscle. 

 The remaining peculiarities will be better understood as we proceed to state in 

 sequence the experiments which led to their discovery. 



Experiment. — A large turtle (snapper) was secured on its back, its mouth held 

 open. It breathed well at intervals of two minutes or more. The recurrent nerves 

 were exposed and galvanized at the middle third of the trachea. Irritation by this 

 agent and by mechanical means, caused the lips of the glottis to open, although not 

 very freely. The two nerves were then divided, and the trachea cut across. The 

 glottic movements continued perfect, and were synchronous with the respiratory 

 motions of the breast-box. The muscles of the right side over the hyoid apparatus 

 were then removed, the covering fascia beneath them dissected off, and the superior 

 laryngeal nerve discovered lying under the shelter of the superior hyoid wing. 

 Irritation of this nerve or its fellow on the opposite side caused the outer edge of 

 the glottic lips to open, while the inner edge appeared to be forcibly closed at the 

 same time. On cutting the nerves across, and stimulating the peripheral ends, like 

 results were observed. 



The left superior laryngeal nerve being intact, galvanization of the centric end 

 of the divided nerve on the right side caused first, closure of the inner lips and 

 opening of the outer lips of the glottis ; and second, violent and general muscular 

 movements and winking, apparently expressive of acute pain. 



Finally the left superior laryngeal nerve was divided, when complete paralysis of 

 the glottis ensued. 



Order of section, ami results: — 



1. Section of both inferior laryngeal nerves, causing glottis to open; glottic 

 movements perfect after section. 



2. Cut right superior laryngeal nerve, causing glottis to open superficially and to 

 close below; galvanization of outer end of nerve caused same result; galvanization 

 of centric end gave signs of sensibility and reflex closure of glottis, and opening 

 of its outer lips. 



