454 AMPHIBIA. 



The liver has a right and a left lobe, the latter again sub- 

 divided. The gall-bladder lies between the right and left 

 lobes ; bile flows into it from the liver by a number of 

 hepatic ducts, which are continued onwards to the duodenum 

 in a common bile-duct. The pancreas lies, in the mesentery 

 between stomach and duodenum, and its secretion enters 

 the distal portion of the bile-duct. The bladder is a ventral 

 outgrowth of the cloaca, has no connection with the ureters, 

 and seems to be homologous with the allantois of Reptiles, 

 Birds, and Mammals. 



Vascular System. — The heart, enclosed in a pericardium, 

 is three-chambered, consisting of a muscular conical ventricle, 

 which drives the blood to the body and the lungs, of a thin- 

 walled right auricle, receiving impure blood from the body, 

 and of a thin-walled left auricle receiving purified blood 

 from the lungs. From each of the auricles blood enters the 

 ventricle. The two superior venae cavse which bring back 

 blood from the anterior regions of the body, and the inferior 

 vena cava which brings back blood from the posterior parts, 

 unite on the dorsal surface of the heart in a thin-walled 

 sinus venosus, which serves as a porch to the right auricle. 

 From the ventricle the blood is driven up a truncus 

 arteriosus, which soon divides into two branches, each of 

 which divides into three aortic arches. Thus we may dis- 

 tinguish five regions in the heart, — the ventricle, the right 

 auricle, the left auricle, the sinus venosus, and the truncus 

 arteriosus. The sinus venosus is the hindmost, the truncus 

 arteriosus the most anterior part. The two auricles are often 

 included in the term atrium, the undivided part of the 

 truncus arteriosus next the ventricle is called the pylan- 

 gium, the more anterior part from which the arches arise is 

 known as the synangium. The truncus arteriosus corre- 

 sponds, in greater part at least, to the conus arteriosus of 

 many fishes. 



As the heart continues to live after the frog is really 

 dead, its contractions can be readily observed. The 

 sinus venosus contracts first, then the two auricles simul- 

 taneously, and finally the ventricle. Although the ventricle 

 receives both impure and pure blood, the structural 

 arrangements are such, as will afterwards be explained, 

 that most of the impure blood is driven to the lungs, the 



