THE RESPIRATORY SYSTEM, INCLUDING THE LARYNX 275 



involves only the air contained in the mouth and pharynx. This is 

 known as bucco-pharyngeal respiration. The second is more compli- 

 cated and involves the lungs, so that it is conveniently referred to as 

 pulmonary respiration. 



More recently Willem (1923 and 1924) has carried out experi- 

 ments on the respiratory movements of the mouth-floor of a large 

 number of Amphibia, both Urodele and Anuran, including Sala- 

 mandra, and has taken tracings of these movements by means 

 of a stirrup placed under the head and attached to a pointer. 

 (Text-figs. I, 2, and 3 are taken from his work.) Text-figure i is one 



Text-Fig. i. A tracing of the movements of the floor of the mouth, taken by means 

 of a stirrup passing under the head, reading from right to left. The ordinates are magni- 

 fied by 5 and the speed is 4 mm. per sec. The change in the level of the tracing is due to 

 a movement of the head. (After Willem.) 



Text-Fig. 2. A tracing of the periodic variations in the amplitude of the pulmonary 

 expirations. Read from right to left. (After Willem.) 



such tracing in which the ordinates, representing the amplitude of 

 the oscillations of the mouth-floor, are magnified by five, the ribbon 

 at the same time passing under the needle at the rate of 4 mm. per 

 second. The movements involved in pulmonary respiration are 

 represented towards the right-hand side of the figure as a deep de- 

 pression in the otherwise more or less regular succession of bucco- 

 pharyngeal movements. Text-figure 2 shows that there is a rhythmic 

 variation in the amplitude of the pulmonary respirations, while text- 

 figure 3 is an enlarged detail of one series of movements involved in 

 filling and emptying the lungs. According to Willem the bucco- 

 pharyngeal respirations occur at the rate of 1 20 per minute and have 

 an amplitude of nearly 2 mm. The interval between successive pul- 

 monary respirations depends on circumstances. When the animal 

 is in a state of repose it is about fifteen minutes, but if the animal is 



