604 EEL-SHAPED SIREN. 



and close to the extremity of each of these open- 

 ings externally, so many processes arise ; the an- 

 terior the smallest, the posterior the largest : their 

 anterior and inferior edges and extremity are ser- 

 rated, and formed into limbri'de : these processes 

 fold down and cover the slits externally, and 

 would seem to answer the purposes of the comb- 

 like part of the gill in fish. 



At the root of the tongue, nearly as far back 

 as these openings reach, the trachea begins, much 

 in the same manner as in birds. It passes back- 

 wards above the heart, and there divides into two 

 branches, one going to each lobe of the lungs. 

 The ilings are two long bags, one on each sidCj 

 which begin just behind the heart, and pass back 

 through the whole length of the abdomen, nearly 

 as far as the anus. They are largest in the middle, 

 and honey-combed on the internal surface through 

 their w^hole length. The heart consists of one 

 auricle and one ventricle. What answers to the 

 inferior vena cava, passes forwards above, but in 

 a sulcus of the liver, and opens into a bag similar 

 to the pericardium : this bag surrounds the heart 

 and aorta, as the pericardium does in other animals : 

 from this there is an opening into a vein which 

 lies above, and upon the left of the auricle, M'hich 

 vein seems to receive blood from the lungs, gills, 

 and head, is analogous to the superior vena cava, 

 and opens into the auricle which is upon the left 

 of the ventricle. The aorta goes out, passing for 

 a little way in a loose spiral turn, then becomes 

 strait, where it seems to be muscular : at this part 



