36 



A X A T O M Y A N 1) I' II Y S I () 1, O Y O F 



2. Section of righl inferior laryngeal nerve; loss of opening power in right lip 



of glottis. 



We inferred from the above stated experiment and the repetitions of it, that no 

 interlateral nerve fibres connected the two inferior laryngeal nerves. Further- 

 more we failed to discover any branch to which such a function could have been 



assigned. 



The object of the very extraordinary and really exceptional arrangements, which 

 we have here pointed out, is not altogether clear. We arrive only at the general 

 conclusion, that the integrity of the glottic function in turtles, appears to have 

 been guarded with unusual care. "Why this should be the case in aquatic chelo- 

 nians it is easy to understand, but the necessity for it in terrestrial species seems 

 to us less obvious, yet it is as perfect in the box turtle as in the emydse 

 and chelonura?. Perhaps the need for such precautions in all may be due to the 

 fact that all retain the inspired air during long periods, even when on land. Paraly- 

 sis of the closing power of the glottis would allow the air to escape instantly, and 

 would oblige the animal to make repeated and therefore laborious inspiratory 

 efforts. Paralysis of the opening power would insure death from apnoea. Hence 

 we have two sets of nerves controlling the opening muscles. One entire set ma\ 

 be destroyed ami yet respiration continue. Even one of those remaining, if 

 these be the upper nerves, may be lost, and still the glottis fulfil its entire duty in 

 the train of breathing movements. Thus, also, in regard to the closing power. The 

 elasticity of the glottic lips is one agent, although but a subsidiary one. Then we 

 have tin' interlateral communication between the two superior laryngeal nerves, 

 which alone can forcibly close the chink of the glottis. By virtue of this true 

 chiasm one of these nerves being injured, the other is ample to effect the normal 

 purpose of both. 



Nor is it less curious to observe how artfully the whole apparatus lias been guarded 

 against accident. 



The lower or recurrent laryngeal nerves lie alongside of the trachea, sheltered by 

 its projecting form. The superior nerves are protected in their course by the supe- 

 rior hyoid cornu, and the larynx and its singular nervous circle are deeply buried 

 beneath, or rather above the strong bony and cartilaginous body of the hyoid bone. 

 Nature seems to have been lavish of expedients for securing the safety of these 

 most important parts. 



Before leaving this portion of our subject, it may not be amiss to state that we 

 have made a number of experiments on birds and mammals, to ascertain whether 

 any such chiasm exists in the glottic mixes of these animals. Hut in all cases 

 section of one motor nerve caused loss of movement in its own side of the larynx, 

 and we therefore conclude that this arrangement does not extend to the classes in 

 question. Whether or not it is to be found in Batrachia and ophidian reptiles, we 

 have not as yet ascertained. 



The remaining physiology of the pneumogastric nerve in turtles is not less obscure 

 than in other animals. As in these latter, so in turtles, it sends branches to the 

 trachea, lunj^s and heart. 



We have cut the nerve in a number of turtles, some of whom survived upwards 



