SANGUIFEROUS SYSTEM. 479 



each side corresponds with that of the branchial organs when 

 developed ; they are generally three in number ; at first they 

 do not appear to communicate with the trunks of the bran- 

 chial veins by anastomosing canals at their base, their trunks 

 being nearly or entirely occupied in the formation of branchial 

 capillaries, and this fish-like character of the branchial 

 arteries of the young tadpole was found by Cuvier also 

 in the adult siren, where the whole blood is thus forced 

 through the gills. The arterialised blood returning 



FIG. 13(>. 



from the gills of the tadpole by the anterior branchial veins, 

 (136.C. c. c.} is in part sent, as in fishes, by ascending branches, 

 (136. l.m.n. o.) to the head and anterior parts of the body, 

 while the rest is collected into larger trunks, (136. d> d.) 

 which unite to form the descending aorta, (136. e.) At an 

 early period of the development of the tadpole, however, 

 minute anastomosing canals are formed or enlarged between 

 the great trunks of the branchial arteries and those of the 

 branchial veins, (136. b. b. g.g,} by which a preparation is made 

 for the gradual obliteration and absorption of the whole 

 branchial apparatus ; and the same canals of communication 

 between these trunks are found to exist in nearly all the 

 perennibranchiate forms of amphibia in their adult state. 

 From the posterior branchial artery on each side, convey- 

 ing venous blood in the earliest condition of the tadpole, 

 a minute branch (136. i.i.) descends to the rudimentary lungs, 

 and in its course unites with an anastomosing trunk (136. h. h.) 

 from the posterior branchial veins conveying the arterialized 

 blood from the gills, to supply these pulmonary organs. 



