72 



H. L. Bruner 



An apparatus for closing the choana is also present in all of 

 the lower urodeles examined [Necturus, Proteus, Siren, Amphiuma 

 and Cryptobranchus) and also in the larvae of higher amphibians. 



The different forras of this choanal mechanism must now be 

 described. 



The Choanal Valve of Necturus. 

 The internal nasal opening of Necturus is a narrow slit which 

 lies near the angle of the mouth, between the palato-pterygoid and 



Fig. 3. 



Necturus macidosus. Trausverse section through choana. Is upper lip; li lower lip • m oral cavity; 



n nasal cavity, v choanal valve, on the median side of the opening, from which a short postnasal 



canal leads to the cavity of the mouth. 



vonier, on one band, and the antorbital cartilage, on the other. 

 When the mouth is closed the mandible lies directly below the choana, 

 but a free passage is left between the opening and the medial part 

 of the oral cavity. This postnasal passage is formed, in part by a 

 depression between the vomer and the palato-pterygoid, in part by 

 a notch in the dorsal margin of the mandible between the dental 

 and splenial bones. From the roof of this passage, on the median 

 side of the choana, hangs ' the valve which Fischer (1864, p. 114) 

 and Anton (1911, p. 182) have briefly described. The valve is a 



