l; ES P I R A T ION 1 N T II E C 11 E LO N l A ;;i 



all the true glottic muscles, and enjo) thus the ability to open and to close this 

 orifice, and that the inferior Laryngeal nerves are the motor nerves of the dilating 

 muscles only, and have not sensibility or power to close the glottis. 



What then is the reason of this double distribution of two nerves to one muscled 

 Upon this question we shall presently return. It seems highly probable that both 

 nerves usually act at once to open the glottis, since galvanization of either set of 

 nerves does not fully effect this end, while, when both sets of nerves are stimulated, 

 the glottis opens wide. 



'The distribution and functions of the two laryngeal nerves in turtles are thus 

 seen to be totally different from what we see in mammals. In them, as we need 

 only to remind the reader, the superior laryngeal is a nerve of sensation chiefly, and 

 although it possesses also a motor filament, this, in man at least, is distributed to a 

 muscle, the crico-thyroid, which has neither homologue nor analogue in chelonian 

 reptiles. In mammals the inferior laryngeal is, as in the turtle, a motor nerve, but 

 it supplies alike the dilating and the closing muscles of the glottis. 



On reference to the anatomical part of this essay, it will be seen thai the hypo- 

 glossal nerve lies close to the track of the superior laryngeal nerve, and might 

 readily be confounded with it, when the intention is to find and divide the latter 

 alone. The nerve in question supplies muscular branches to the tongue only. 



Thus far the physiology of the glottic nerves in turtles, although determined 

 for the first time, and shown to present points of great interest and novelty, has 

 not exhibited any peculiarity so exceptional as that to which we shall now direct 

 attention. 



This was brought to our notice while further pursuing the study of the functions 

 of the glottic nerves. The mode in which it was first suspected, then discovered, 

 and finally set in clear light by every available means, will be best set forth in the 

 following record of our experiments and inferences, in the order in which they 

 occurred. 



Experiment. — A small snapper, one and a half pounds in weight, was secured as 

 usual. Its respiratory acts observed to be perfect, and the two inferior laryngeal 

 nerves divided one after the other, causing twitching of the glottic lips. After this 

 the glottis still opened and shut as before, and, indeed, equally as well. It was 

 plain, as Ave have already seen, that the superior laryngeal nerves could open and 

 shut the glottis without other aid. Next, the right superior laryngeal nerve was 

 cut at the middle of the upper hyoid cornu, and the glottis was carefully observed. 



The section caused twitching of the glottic lip, and at the next respiration, to our 

 great surprise, both sides of the glottis, the right as well as the left, opened equally 

 well. In fact there was no difference. A close inspection satisfied us that the 

 section of the nerve was complete. 



If now we recall the facts, that the glottis of both sides was moving despite the 

 section of both recurrents and one superior laryngeal nerve, it will be seen how 

 mysterious this must have appeared to those who first observed it. We came to 

 the conclusion either that there existed some mechanical arrangement of the glottis 

 and its muscles, which enabled one side, while in motion, to communicate that 

 movement to the other, or. that there was a direct nerve communication between 



