When the ramification of the entodermal tubes into the lung mesoderm is complete, the 
small terminal flask-shaped extremities of the various branches represent the infundibula. 
At first these are devoid of air-cells, but between the sixth month and the termination of 
gestation the alveolar diverticula make their appearance on the alveolar ducts and on 
the infundibula. It is thus seen that the epithelial lining of the entire system of bronchial 
tubes, infundibula and alveoli, is originally derived from the entodermal lining of the fore- 
gut. The other constituents which enter into the constitution of the lungs and bronchi 
are derived from the mesoblast. | 
The rudiments of the lunes grow backwards on either side of the cesophagus into the | 
fissure-like portion of the caeelom which occupies the thoracic region. They push before 
them the epithelial lining of the latter, and thus acquire their covering of visceral pleura. 
By the development of the diaphragm and the pericardium the pleural portions of the 
ceelom become cut off from the peritoneal cavity and from each other. Our knowledge 
-of the development of the lungs has been greatly extended by the writings of Professor 
His and Professor Arthur Robinson. 
