484 SANGUIFEROUS SYSTEM. 



auriculo-ventricular orifices. The auricles are more advanced 

 over the upper and fore part of the ventricle, than the aurcle 

 even of the plagiostome fishes, and the whole heart, like 

 that of fishes, is situated further forwards towards the head 

 than in reptiles or the warm-blooded vertebrata. The ven- 

 tricle was observed by Meek el to be partially divided by an 

 internal septum extending from the apex in the pipa, as in 

 chelonian reptiles, and he also observed the septum between 

 the auricles in the pipa, the siren and the axolotl, without 

 perceiving the difference of function in these cavities dis- 

 covered by Davy and Weber in both these orders of amphi- 

 bia. The sinus venosus of the right auricle and the bulbus 

 arteriosus or commencement of the aorta, are here distinctly 

 muscular and contractile, like the corresponding sinus and 

 aortic bulb in the plagiostome and other fishes. 



The two aortic trunks meet behind, under the vertebral 

 column, as in reptiles, to form the abdominal aorta, at a point 

 more or less advanced towards tlie head in different species, 

 and in their course backwards, these two aortic vessels com- 

 municate with the trunks of the pulmonary arteries by means 

 of the two ductus arteriosi. From the commencement of each 

 of the two aortic trunks, a large artery originates, which 

 divides into a brachial and a cephalic branch, to supply the 

 corresponding arm and side of the neck and head, and these 

 primary brachio-cephalic branches of the aorta, commonly 

 supplying the anterior parts of the body in the amphibia, have 

 the same size and mode of distribution on the right and left 

 sides. The next great trunks from the arches of the aortee, are 

 the two pulmonary arteries, which descend on each side to 

 ramify chiefly on the dorsal and median surfaces of the lungs, 

 and which vary in size in different species according to the 

 development of these pulmonary sacs. The bulb of the 

 aorta often presents a rounded dilatation in the adult, cor- 

 responding with the part from which originated the bran- 

 chial arteries of the larva. At the commencement of the 

 great trunk of the abdominal or descending aorta, in the 

 anourous species, the cseliac or common visceral artery 

 arises, as in fishes, which gives off the gastric, the hepatic, 

 the mesenteric, and other arterial branches, to supply most 

 of the chylopoietic organs. The common trunk of the aorta 

 gives off several small vessels to the kidneys and the geni- 



