406 DAVIDSON BLACK 



importance of gustatory components within this area in urodeles 

 may no doubt in part account for the caudal position of the VII 

 motor nucleus in these animals, as Kappers has suggested. 



Mechanics of respiration. A study of the mechanics of res- 

 piration brings out the fact that neither the acquisition of the 

 pulmonary type of respiration nor the retention of the aquatic 

 type of respiration appears in itself to be a factor of importance 

 in determining the motor nuclear pattern. 



Baglioni's observations (4, 5) on the respiratory movements 

 in the adult frog may be briefly summarized as follows: Two 

 varieties of respiratory movements occur, (a), laryngeal move- 

 ments of a rythmical oscillatory nature which by alternate 

 elevation and depression of the bucco-pharyngeal floor provide 

 for constant renewal of the air within this cavity, and (b), 

 'proper' respiratory movements at longer intervals which bring 

 about the renewal of the pulmonary air. In the 'proper' re- 

 spiratory movements three distinct phases may be recognized. 

 The first phase (aspiration) begins at the end of one of the 

 rhythmical laryngeal movements when the floor of the mouth is 

 depressed, and results in a further active dilation of the bucco- 

 pharyngeal cavity. Towards the close of this active dilation, 

 the glottis is opened and air is forced out of the lungs into the 

 bucco-pharynx while at the same time the nares are closed. 

 The passive enlargement of the bucco-pharynx by the expulsion 

 of the pulmonary air marks the close of the second phase of 

 the respiratory act (expiration). Immediately following ex- 

 piration the tongue is thrust against the roof of the mouth, 

 the choanae are closed by the hyoid cornua, the bucco-pharyn- 

 geal floor is strongly elevated and air is forced through the 

 glottis into the lungs (inspiration). On the completion of the 

 inspiratory act the glottis is closed and remains in this condi- 

 tion while the oscillatory laryngeal movements begin anew. 



Among urodeles pulmonary respiration takes place in a man- 

 ner essentially similar to that obtaining in anurans, and the 

 same three phases (i.e., aspiration, expiration and inspiration) 

 may he recognized in each complete respiration (v., Briiner, 

 12, 13, 14; Camerano, 15; Wilder, 60, 61). Further, aquatic 



