181 



the lateral and dorsal areas of the lung are completely adherent 

 to the corresponding surfaces of the parietal pleura (10). 



The adhesion is obtained by the same formation of loose connec- 

 tive tissue and loss of surface epithehum as occurs in the elephant. 



That respiration is not impeded l)y simple obliteration of the 

 pleural cavity is evident in view of the fact that recent complete ad- 

 hesion of lung to surrounding structures may occur in man without 

 exhibiting clinically any respiratory symptoms revealing its presence 



Fig. 3. Transverse section of large intrapulmouary bronchus from lung of 

 Herpesteti. for comparison ^vith fig. 2. magnified 47 diameters. Note presence of 

 cartilaginous flakes, a 



or extent. This does not, of course, refer to a chronic pleurisy of some 

 standing. 



The partial absence of pleural cavity in birds is not comparable 

 to the absence in proboscideans because of the entirely different 

 respiratory mechanism of the avian lung and air sacs. 



It is possible that the absence of intra-pulmonary bronchial 

 cartilages in the elephant is connected with the absence of pleural 

 cavity in some such manner as has been already suggested. On the 



