16 Observations on the Natural History 



small cleft or chink, the margins of which do not rise above the 

 surface, nor possess a cartilaginous structure. This very small 

 chink or glottis, as it may be called, communicates with a very 

 short canal, which proceeds backwards above the heart, between 

 the pericardium and pharynx. This canal exteriorly, and on 

 the side next the heart, is furnished with two very fine muscu- 

 lar expansions, the fibres of which springing from the median 

 line of the canal itself, are disposed like the beard of a pen, and 

 directed back towards the branchial arches. The office of this 

 very subtile muscular substance is, doubtless, that of dilating the 

 canal, and opening the glottis. The canal itself, before getting 

 beyond the heart, opens, by a semilunar aperture, which has car- 

 tilaginous margins, into a large conical cavity, Plate VII. Fig. 2. 

 From this funnel-shaped cavity, are continued two membranous 

 canals, which, keeping the stomach between them, descend towards 

 the tail : but before reaching the lower-third of the trunk, they 

 begin to dilate, and by degrees expand, so as to acquire the form 

 of two small flasks ; the left descending a little lower than the 

 right. These two canals are attached to the spine, by duplica- 

 tures of the peritoneum, in which, through their whole length, 

 they are involved. The two little flasks or bladders have no 

 . cells nor partitions internally, but are perfectly smooth mem- 

 branes. Were it possible to dilate the two canals to the size of 

 the bladders in which they terminate, these organs would then 

 acquire very exactly the form of the lungs of the salamander. 

 The two bladders are situated one on each side of the abdomen ; 

 that of the left side is represented in Plate VII. Fig. I., and also 

 the narrow canal leading to it. In protei that have been some 

 time in spirits, the canals become entirely closed and quite imper- 

 vious to air ; but in thos? recently dead, the J}ladders are easily 

 dilated by air blown through the canals. 



The authors having observed, that, when a living frog or sala- 

 mander is laid on his back, the abdomen then opened, and its 

 walls fastened back, the lungs, during the struggles the animal 

 makes, sometimes dilate and contract for a certain time, were 

 desirous of ascertaining, by a similar experiment, if the small 

 portion of air which the proteus takes into the mouth found its 

 way into the two little bladders above described. A proteus 



