662 PHYLUM CHORDATA : CLASS AMPHIBIA 



ported by two arytenoid cartilages, and also by a ring ; with 

 the arytenoids the vocal cords are closely associated. The 

 lungs lie so near the mouth that laryngeal, tracheal, and 

 bronchial regions are hardly distinguishable. On the floor 

 of the mouth is the hyoid cartilage, which serves for the 

 insertion of muscles to tongue, etc. 



Of the (4) gill-clefts which are borne on the walls of the 

 pharynx in the tadpole, there are no distinct traces in the 

 adult. The lungs develop as outgrowths from the gullet. 



The gullet leads into a tubular stomach, which is not 

 sharply separated from it. There is a pyloric constriction 

 dividing the stomach from the duodenum, or first part of 

 the small intestine. After several coils the small intestine 

 opens into the wider large intestine or rectum, which enters 

 the cloaca. 



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 duo- 

 denum 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 connec- 

 tion 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 ven- 

 tricle, 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 cavae 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 

 the conus arteriosus into an extremely short ventral aorta 

 which divides into two, each branch consisting of three 

 vessels leading to lungs, body, and head, and bound to- 

 gether for some way along their course. 



