VASCULAR SYSTEM. 541 



on the floor of the mouth is the glottis, the opening of the 

 short larynx which leads to the lungs. The larynx is sup- 

 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 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 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 a 

 truncus arteriosus, which soon divides into two branches, 

 each of which divides into three aortic arches. 



