and Structure of the Proteus Anguinus. S.3 



off on each side by the trunk that springs from the lieart, as 

 there are branchial arches, viz. four. In the siren and axolotl, 

 (which have also eight branchial arches,) M. Cuvler speaks 

 only of six arteries, three on each side, going to the gills ; but 

 as, by the aid of injections, we have found, say the authors, that, 

 in the larvae above named, there are eight vessels, and that the 

 artery which runs along the interior arch of each side, and 

 which M- Cuvier has not seen, is that which in process of time 

 becomes the pulmonary artery, so, guided by analogy, we hold 

 it for certain, that, as the siren is furnished with eight bran- 

 chial arches entirely similar to those of the other larvae, there 

 are also eight arteries, four on each side, corresponding to 

 them. And, proceeding on this opinion, we may remark a 

 striking difference in the circulating system of the siren and 

 proteus, since the artery, properly called Pulmonary, which is 

 found in the siren and larvae above mentioned, does not exist in 

 the proteus. Doublless in the proteus, the air-bladder, like 

 every other part of the body, is du]y supplied with blood ; but 

 the blood sent to it is furnished by an artery coming off, on each 

 side, from one of the aortic trunks, and which artery, descending 

 along the canal of the bladder, gives to it a branch, and is then 

 continued to the ovary or testicle in each sex respectively. 



Besides these diiferences in the arterial, there are others in 

 the venous system ; for the vessel wliich returns the blood from 

 the air-bladder of the proteus, does not empty itself dii-ectly 

 into the cava or the auricle, as is observed in other reptiles ;, 

 but into the vein which carries back the blood from the organs 

 of generation, which itself enters the cava above the middle of 

 the kidney ; hence in the proteus, not only the true pulmonary 

 artery, but the vein also, is wanting. This ariatomical fact, ascer- 

 tained by repeated injections, might alone be sufhcient to de- 

 monstrate, that the two air-bladders with which the proteus is> 

 furnished are not true lungs : but as some, perhaps, may not 

 yield to the force of these arguments, we shall continue the 

 comparison, especially as applied to the organs of respiration. 



In the larvae of the frog and salamander, the trachea opens; 

 directly into the lungs. These organs have the form of two 

 sacs, and, from being longer than the trunk, cannot be extend- 

 ed in a straight line througli it, but at the lower end are folded 



