1.] 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 vein, 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 (cricoid) which 

 supports the wall of the very short laryngeal chamber. 

 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 which 

 lines the faces of the longitudinal 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 produced. 



Laterally the laryngeal 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 pro- 

 duced 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 



