570 AMPHIBIA. 



The internal ears have the usual parts, and lie within the 

 auditory capsules, which are in great part bounded by 

 the pro-otics. Connecting the fenestra ovalis of the ear 

 with the tympanic membrane, which is flush with the skin, 

 there is a delicate bony rod the columella. This lies in the 

 Eustachian tube, which opens into the mouth at the corner 

 of the gape. 



The nostrils open into small nasal cavities, with folded 

 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 

 premaxillae, 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 resonating sacs which open into the mouth cavity at the 

 angle of the jaw, and are dilated during croaking. The 

 tongue bears numerous taste papillae. Behind 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 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 



