Tlie Smooth Facial Muscles of Anura and Salamandrina. 345 



however, the mode of union of the two partes mentales of the den- 

 talia is particularly favorable, while the intermaxillaria offer no 

 appreciable resistance. Their palatine portions are elevated by the 

 tuberculum praeling:uale, the median margin of each palatine portion 

 describing a small arc about the lateral margin as a center, and 

 thus is set in motion the mechanism immediately concerned in clos- 

 ing the external nares. 



From the foregoing, which is based chiefly on a study of Rana 

 fusca Rös. and Rana i)ipiens Gmel. , I am led to conclude that the 

 external nares of the frog may, under ordinary conditions, be closed 

 either by protraction of the lower jaw alone, or by the simple con- 

 traction of the submentalis muscle. It is probable, however, that in 

 normal respiration these two modes of closing the external nares 

 supplement each other to a considerable extent; while either method 

 is employed with greater energy when the other is not in use. In 

 the case of protraction this is easy to observe after elimination of 

 the submentalis, as already described above. In violent inspiration 

 both methods of closing the external nares are simultaneously employed 

 to their fullest extent. The special value of protraction as a 

 mode of closing the external nares lies in the fact that it 

 assists at the same time in maintaining a close contact of 

 the jaws. The submentalis muscle alone is an effective agent in 

 closing the external nares, but its contraction creates, at least in 

 strong respiration, a necessity for protraction of the lower jaw, in 

 order that the intimate union of the two jaws may not be 

 disturbed. 



In Hyla (H. versicolor Le Conte) I find the protraction of the 

 lower jaw quite as marked as in Rana. In Bufo (B. lentiginosus 

 Shaw), on the other hand, I was able to detect only a trace of pro- 

 traction until the nerves supplying the submentalis had been cut, 

 when the movements became strong and regular with each inspiration. 

 The unimportant part played by protraction in the ordinary respiration 

 of Bufo I attribute to the absence of teeth, by reason of which the 

 close contact of parts during inspiration is more easily maintained 

 by the elastic upper lip. 



The above conclusion in regard to the function of the lower jaw 

 in connection with the closing the external nares of Rana agrees in 

 the main with the observations of Gaupp (20), who recognized the 

 fact that the contraction of the masticatory muscles affects the entire 

 lower jaw, including its rostral portion, and that therefore the closing 



