and Structure of the Proteus Anguinus. 15> 



the blood by the vessels given off from the aorta, it is unneces- 

 sary to say more ; but of the return of this blood to the heart 

 by the veins, it is proper to take some notice. 



There are three principal veins which reconvey the blood from 

 the different parts of the body to the heart ; two corresponding 

 to Xhe jugulars, and the third to the ascending vena cava. The 

 two former, after receiving the blood which returns from the 

 head, pour it into the cava, where that vein is so dilated as 

 to form a sort of sinus. Into the cava, also, at different parts, 

 is poured all the blood returned from the trunk. Thus two 

 large veins which ascend the spine on each side of the aorta, 

 and receive the blood of the dorsal veins in their progress, 

 enter the cava much below the middle of the trunk. The blood 

 of the air-bladder and organs of generation is poured, by a 

 single vein, into the cava about the middle of the kidney. The 

 vein which collects the blood from the intestines, arises near the 

 termination of the alimentary canal ; and proceeding between the 

 expanded portions of the peritonaeum that form the mesenteiy, 

 gains the neighbourhood of the stomach : there its trunk, which 

 may be called the vena porta, is spread entirely through the 

 concave surface of the liver. After circulating through that 

 viscus, the blood is again collected into one vein, which, travers- 

 ing the edge of the liver, pours its blood into the cava at the 

 point where that vessel itself quits the liver to continue its course 

 to the auricle. 



6. Of the Organs of Respiration. 



In the preceding chapter on the organs of circulation, the 

 authors have described, with all the accuracy they were able, the 

 course of the branchial arteries and veins to and from the ^lls, 

 which might be considered as including a description of the res- 

 piratory organs ; but as iheproteus anguinus, besides being fur- 

 nished with gills, is provided also ^vith Xwo air-bladders, which, 

 from a resemblance to the lungs of the aquatic salamander, have 

 been regarded as two real lungs, it is necessary to give a more 

 particular description of those two organs. 



In the bottom of the fauces, and exactly in the middle of 

 that space which lies between the branchial apertures which 

 communicate with the gills of each side respectively, there is a 



