The Smooth Facial Muscles of Anura and Salamandrina. 357 



cance. a) The elevation of the tuberculum praelinguale involves, to 

 a certain extent, the withdrawal of the two halves of the lower jaw 

 from close contact with the dentary processes of the upper jaw bones. 

 Such a withdrawal is prevented by the protraction of the lower jaw 

 at the moment of closing the external nares. b) The tuberculum 

 praelinguale may be elevated also as a direct result of the protraction 

 of the lower jaw. In this manner the closing of the external nares 

 is effected without the cooperation of the musculus submentalis. 



9) The retraction of the lower jaw of Rana after inspiration is 

 probably due to elastic forces only, among which the most important 

 are, a) the elasticity of the ligaments at the articulation of the lower 

 jaw with the skull, b) the tension of the musculus labialis superior, 

 and c) the elasticity of the intermaxillary apparatus for closing the 

 external nares. 



10) Although the immediate cause of the closing of the external 

 naris in Rana is a movement of the cartilago alaris, smooth nasal 

 muscles are present in the neighborhood of the naris, and these 

 perform a minor function in connection with the closing of the 

 aperture. 



11) One of these nasal muscles of Rana is homologous with the 

 dilatator naris of Triton and gives tension to a fold (plica obliqua) 

 against which the cartilago alaris presses in closing the naris. 



12) A second muscle of Rana, more superficial in position than 

 the dilatator naris, is in all probability a homologue of the constiictor 

 naris of the salamander. In Rana the constrictor naris acts as a 

 tensor and retractor of certain parts adjacent to the external naris; it 

 probably serves also as a compressor of the glandula nasalis externa. 



1 3) An examination of the descriptions of Zenker, Collan, and 

 their followers affords no evidence that the mm. dilatator naris and 

 constrictor naris of Anura were observed by these investigators. 



14) The nasal muscles of Rana seem to maintain a steady tension 

 which changes little or none during the various phases of respiration. 



15) Traces of the nasal muscles are to be found also in Alytes, 

 Hyla, and Bufo, but among the forms investigated these muscles 

 show the highest development in Rana. The degeneration of the 

 nasal muscles in other forms is accompanied by the development of 

 a bony support for the plica obliqua. 



16) The development of the nasal muscles and of the external 

 nasal gland of Rana resembles that of the homologous parts in 

 Triton. 



