The Mechanism of Pulmonary Respiration in Ainphibians with Gill Clefts. 73 



triangulär fold of mucous membrarie (Figs. 3, 4, and 5) which is 

 attached to tlie median and posterior margins of the opening. Its 

 anterior angle extends forward a short distance in front of the 

 opening and inserts in the connective tissue behind the lateral portion 

 of the premaxillary bone. The valve is not provided with rnnscles 



Fiar. 4. 



■ Fisr. 5. 



Fig. 4. Nectttrus maculostts. Choaial region, with the choanal valve open. The anterior end of 



the valve is inserted under a fold of mucous membrane which is pushed aside to show the attachment. 



Is upper lip; ppt palato-pterygoid ; v choanal valve; to vomer. 



Fig. 5. Neclnrits maculosits. Choanal valve closed. 



and acts in a purely mechanical way, being opened by pressure of 

 the respiratory medium in the nasal cavity, while it is closed by 

 any movement of the respiratory medium through the postnasal 

 passage toward the choana. 



The function of the choanal valve of Necturus has been tested 

 by cutting away the entire left valve in a large specimen, which 

 was then placed in a shallow dish and covered with water. The 

 normal respiratory movements, both branchial and pulmonary, were 

 promptly resumed. At each pulmonary respiration a certain amount 



