540 AMPHIBIA. 



walls of sensitive membrane ; the posterior nares open into 

 the front of the mouth. 



There are taste papillae on the tongue, and touch spots 

 on the skin. 



Alimentary System. 



The frog feeds in great part on insects, which it catches 

 dexterously with its tongue. This is fixed in front and loose 

 behind. There are teeth on the pre-maxillae, maxillae, and 

 vomers. Into the cavity of the mouth the nasal sacs open 

 anteriorly, and the Eustachian tubes posteriorly. The males 

 of Rana esculenta have a pair of sacs which open into the 

 mouth cavity at the angle of the jaw, and are dilated during 

 croaking. The tongue bears numerous taste papillae. Be- 

 hind the tongue on the floor of the mouth is the glottis, the 

 opening of the short larynx which leads to the lungs. The 

 larynx is supported 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, &c. 



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. 



