CH. VIIl] FllOGS, TOADS, AND NEWTS 263 



close meshwork with frequent irregular dilatations of the 

 walls. This peculiarity would cause the blood to pass 

 very slowly through the capillary plexus and give more 

 time for the respiratory interchange of gases. 



To understand the more extensive muscular move- 

 ments by which the pulmonary respiration is brought 

 about, it is necessary to bear in mind, (1) that the lungs 

 are elastic and that their natural tendency is to expel air 

 from their cavities ; (2) that there are no firm thoracic 

 walls by which pressure may be removed from the outer 

 surface of the lungs, and therefore (3) that air must be 

 forced down into the lungs by some mechanism acting 

 along the air passages themselves with sufficient power 

 to overcome the elastic recoil of the walls of the lungs. 

 For our knowledge of the phenomena we are chiefly 

 indebted to the researches of Bert 1 , Gaupp 2 and Baglioni 2 . 

 Three distinct phases are recognisable in these movements, 

 (1) aspiration of air through the nostrils into the cavity 

 of the mouth : this is brought about by lowering the floor 

 of the mouth, the glottis remaining in its resting position, 

 i.e. closed; (2) expiration of air from the lungs into the 

 enlarged mouth cavity ; this is achieved by opening the 

 glottis, and by the contraction of the abdominal muscles 

 and of the walls of the lungs ; (3) inspiration or 

 injection of air into the lungs by closing the nostrils, 

 keeping the glottis open, and raising the floor of the 

 mouth. This action can be detected externally by the 



1 Legons sur la Physiol. compares de la respiration, Paris, 1870. 



2 Gaupp, Arch.f. Anat. undPhys. (Anat. Abth.), 1896; Baglioni, ibid. 

 (Physiol. Abth.), 1900, Supp. Bd. 



