68 H. L. Bruner 



escapes from the nostrils or spiracle during the act of inspiration. 

 The surplus air which remains in the mouth after inspiration is 

 expelled between the lips. Water is evidently retained in the nasal 

 cavity during the entire pulmonary process. 



The Respiratory Mechanism. 



The preceding observations show that the respiratory movements 

 of amphibians with gill clefts are very similar to those of higher 

 amphibians. They also indicate the existence of a very definite me- 

 chanism for the control of the respiratory media, although evidence of 

 more or less Variation has been found in difTerent forms. In the 

 following description of this mechanism special attention is given 

 to parts hitherto unobserved and to those whose connection with the 

 respiratory process has not been emphasized. I include here, especi- 

 ally, the arrangements for closiug the mouth, gill clefts and nasal 

 openings. The more couspicuous muscles of the mouth and pharynx 

 have been described. 



The Closing of the Mouth. 



When the mouth is filled with air or water the elevation of the 

 floor of the cavity tends to separate the jaws. This is chiefly pre- 

 vented by a tonic condition of the adductor muscles of the mandible 

 and by close contact of the lips (see Fig. 3). If the adductor muscles 

 are cut on one side of the head, bubbles of air escape from the 

 mouth on the operated side, especially during the stronger inspira- 

 tions. Similar losses were observed after the upper and lower lips 

 were divided on one side at a point midway between the rostrum 

 and the angle of the mouth, the adductor muscles being in a normal 

 condition. In all of the urodeles studied the lips have the same 

 general form and they probably have the same function in connec- 

 tion with respiration. 



In Necturus and Siren the retraction of the lips seems also to 

 be an important factor in closing the mouth. Electrical Stimulation 

 of the masseter muscle causes both adduction of the mandible and 

 retraction of the two lips and the same effect undoubtedly follows 

 the contraction of the muscle under natural conditions. In Necturus 

 this is apparently due to a close union of the sheath of the muscle 

 with the connective tissue of the lips at the angle of the mouth. 

 In Siren a bündle of fibres from the masseter is inserted at this point. 



