I.] THE FROG. 21 



the blood from the alimentary-canal and its appended 

 glands, with the spleen. This vessel enters the liver 

 on the left side, breaking up within that organ; before 

 doing so, it enters into a direct anastomosis with the 

 anterior abdominal vein. 



5. The system of the pulmonary veiJi, formed by the 

 union of the veins of the right and left lungs. 



The slit-like glottis of the Frog is formed by the appo- 

 sition of two longitudinal folds of the mucous membrane 

 of the mouth, each of which contains a cartilage of similar 

 form. These cartilages are the arytenoid cartilages. They 

 are articulated with an annular cartilage {laryngo-tracheal) 

 which supports the wall of the very short chamber which 

 represents the larynx and trachea. When the two folds of 

 the glottis are divaricated, there are seen between them two 

 membranous pouches, the free edges of which meet in the 

 middle line, while anteriorly and posteriorly they pass into 

 the mucous membrane v/hich lines the faces of the longitu- 

 dinal folds. These are the vocal ligaments, and the slit 

 between them is what answers to the glottis in Man. 

 It is by their vibration that the croak of the Frog is pro- 

 duced. 



Laterally the laryngo-tracheal chamber opens into the 

 lung of each side. The lung is a transparent oval sac, 

 somewhat pointed posteriorly, which lies at the side of the 

 oesophagus in the anterior region of the pleuroperitoneal 

 cavity. It is covered by a layer of the pleuroperitoneal 

 membrane which represents the visceral layer of the pleura 

 in the higher animals. The wall of the pulmonary sac is 

 produced inwards so as to give rise to a network, which is 

 much more prominent in the anterior than in the posterior 

 part of the lung and divides the periphery of the cavity 



