K i; s r 1 R A T I N I N T II i: C U E I. N I A . 2g 



The author to whom we have alluded as the onlj one who has approached to a 

 clear comprehension of the true mechanism of respiration in turtles is Robert Town- 

 son, LL. D.' The anatomy of the respirator} muscles of the breast-box is 

 described by this author, as we have elsewhere shown, with much correctness. His 



statement as to the mechanism of the movements of the chest and bell) muscles in 



breathing are, also, remarkably truthful, and are approached in this particular b) 

 those of no other or later authors. 



He came to the conclusion, as we have seen, p. 6, that the turtle and frog do aol 

 breathe alike, hut that while the latter forces air into the lungs, the former 

 possesses a type of respiratory movement closely analogous to that of the mammal. 



He described an inspiratory muscle in the posterior flanks, and an expiratory 

 muscle covering the hack of each lung, and attached to a broad tendinous expan- 

 sion, running forward, to be inserted in front on the carapace, above the lung. 

 To do full justiee to this most ingenious and neglected observer, we have 

 quoted, in connection with the anatomy of our subject, the experiments, by 

 means of which he proved that turtles do not force air into the lungs, p. G, and 

 by which he also showed that they draw the air into the chest, by muscles attached 

 to the breast-box, and expel it through the aid of the expiratory muscle covering 

 the posterior end of the lung. 



Considering the period at which lie wrote, nothing could be clearer than the 

 above statement, and we are amazed, that its obvious truth should have so long 

 escaped recognition. 



In the summer of 1861, one of us, Dr. Weir Mitchell, while engaged in studying 

 the blood-pressure in the snapping turtle, Chelydra serpentina, became convinced 

 that the prevailing views as to the respiratory mechanism of Chelonian reptiles 

 were totally incorrect. Accordingly he partially studied the subject, and incident- 

 ally embodied his opinions in an essay upon the blood-pressure in the snapping 

 turtle. 2 At the time referred to, Dr. Mitchell was unacquainted with Townson's 

 researches. The views of Dr. Mitchell, and the experiments by which he supported 

 them, will be found scattered through the text of the present essay, of which, indeed, 

 they form the basis. In the summer of 1862, the present authors took up anew the 

 study of the respiration in turtles, and have endeavored to render it as complete 

 as possible. In so doing they have been fortunate enough to carry the subject far 

 beyond the crude experiments of Townson, and to discover anatomical and physiolo- 

 gical facts of the utmost interest and novelty, which have hitherto escaped attention. 



To facilitate the comprehension of the subject, we shall divide the physiological 

 part of this essay in the following manner : — 



1st. The externally visible phenomena of respiration. 



2d. Physiology of the muscles of respiration. 



3d. Physiology of the respiratory nerves. 



1 Tracts and Observations in Natural History in Physiology. London, 1799. Cuvier's views 

 and his criticism of Townson may be found appended to the full quotation of Townson's dissertation, 

 at p. 6 of this essay. 



* American Phil. Trans., Phil. 1882. 



