318 Henry L. Brauer 



it seems also desirable to recall the general characteristics of the 

 respiration of the lungbearing Amphibia. 



The investigation which has furnished the basis of the present 

 paper was begun in the Anatomical Institute of Professor Wieders- 

 HEiM, whose esteemed counsel during uiy stay in Freiburg it gives 

 me pleasure to acknowledge here. 



I. The Respiratory Mechanism of Ampliibiaus with Limgs. 



In the absence of ribs and diaphragm, both Anura and Sala- 

 mandrina are unable to inflate the lungs by an active enlargement 

 of the thorax. In place of the thoracic suction-pump of higher ver- 

 tebrates we find, accordingly, in amphibians a bucco-phar^'ngeal 

 force-pump, by means of which the air is forced into the lungs by 

 contraction of the bucco-pharyngeal muscles. These movements of 

 inspiration, which occur at somewhat irregular intervals, are imme- 

 diately preceded by expiration, which begins with the opening of 

 the aditus laryngis and is completed by the contraction of the ab- 

 dominal muscles, by which the air from the lungs is forced into the 

 bucco-pharynx. From this chamber a part of the air passes out 

 through the nose, but a part also remains to mix with air already 

 in the mouth before expiration began. Immediately after expiration 

 is ended and while the aditus laryngis is still open, occurs inspiration, 

 which is inaugurated by the closing of mouth and external nares, 

 and completed by the contraction of the bucco-pharyngeal muscles 

 and the closing of the aditus laryngis. Thus the mixed air found 

 in the mouth at the close of expiration is forced into the lungs and 

 retained until the next expiration begins. In the intervals between 

 these proper respiratory movements occur somewhat regular oscillations 

 of the floor of the mouth and pharynx, during which the external 

 nares remain open. These bucco-pharyngeal movements serve a 

 double purpose. The frequent changes of air tend to remove the 

 expired air which might have remained in the bucco-pharynx after 

 inspiration, and thus preparation is made for the next inspiration 

 which immediately follows an ordinary inflation of the bucco-pharynx. 

 Secondly, the ventilation of the bucco-pharynx has in itself a res- 

 piratory significance, for it facilitates the purification of the blood in 

 the capillaries of the oral and pharyngeal mucous membrane. The 

 effectiveness of this made of respiration is greatly increased, as 

 shown by Mauker (35) and Bethge (3), by the vascularization of 



