.The Smooth Facial Muscles of Anuni and Salamandrina. 343 



nasales superiores, and third, a movement in a median direction 

 of the posterior end of each cartilago alaris, whereby the external 

 nares are closed. These movements are naturally all reversed during 

 the depression of the palatine portions of the intermaxillaria. This 

 mode of closing the external nares may be easily observed in a 

 recently killed frog, if a slight upward pressure be applied to the 

 tip of the rostrum. 



d. Function of Parts. 



The adduction of the lower jaw by the masticatory muscles 

 forms a natural starting point for the consideration of the function 

 of the various parts of the mechanism for closing the external nares 

 of Rana; for the contact of the jaws, at least at the rostrum, is a 

 condition prerequisite to the closing of these openings. With the 

 jaws in contact, the nares may be closed, as known already to 

 DuGES (15), by the submentalis muscle [M.s.^ Fig. 10, PI. XVII), 

 which lies beneath the rostrum and spans the angle between the 

 two partes mentales of the dentalia. It has been shown by Gaupp 

 (20), that when the mouth of Rana is closed, electrical stimulation 

 of the submentalis produces immediate closing of the nares. The 

 manner in which this function is performed may be understood if 

 the mouth of a living frog be held open [e.g., by a stout cord between 

 the jaws) so that the partes mentales of the dentalia are freely 

 exposed. When the animal attempts to inspire, the submentalis may 

 be seen to contract, the angle between the two partes mentales of 

 the dentalia becomes more acute and the tuberculum praelinguale is 

 thrown forward and upward. When the mouth is closed the direction 

 of this motion is modified by the upper jaw and lip, and the move- 

 ment is converted into an elevation of the tuberculum praelinguale 

 against the fossa subrostralis media. 



After the above explanation of the action of the submentalis 

 in closing the external nares of the frog, we are in a position to 

 understand the significance of protraction of the lower jaw as a 

 factor in preventing the separation of the two jaws during inspiration 

 (see page 335). It is evident that the mere elevation of the tuberculum 

 praelinguale involves a drawing together toward the median line of 

 the two halves of the lower jaw, especially their anterior parts, and 

 the consequent withdrawal of these parts from close contact with the 

 dentary processes and teeth of the maxillaria and intermaxillaria. In 

 this manner, however, the union of the jaws would be weakened, and 



