472 WILLIAM A. LOCY AND OLOF LARSELL 



The connection between the anterior intermediate and the me- 

 sial moiety of the interclavicuhir sac is well exhibited. The fork 

 (shown in other figures) on the distal end of the mesial moiety 

 is not visible owing to the position in which the specimen is 

 viewed. It curves around the main bronchus away from the 

 observer. The common opening (interclavicular canal) into the 

 third entobronchus, of the anterior intermediate and the mesial 

 moiety is well exhibited in this specimen. 



The external appearance of the lung on the thirteenth day of 

 development is shown in figures 22 and 23, in which the lung of 

 the left side is sketched as exposed by dissection within the 

 thoracic Qavity (fig. 22) and both right and left lungs sketched 

 on a larger scale as removed from the thorax (fig. 23). The 

 points to be noted are: the lateral position of the lungs in the 

 thoracic cavity; the deep indentations of the ribs on the latero- 

 dorsal border; the presence of five air-sacs with the stems of the 

 recurrent bronchi from the abdominal and the posterior inter- 

 mediate air-sacs. The mesial moiety of the interclavicular sac 

 is hidden by the curvature of the lungs. On the surface of the 

 right lung is seen a clear space between the abdominal and the 

 posterior air-sacs. This probably corresponds to the accessory 

 sac of figure 21. 



The most significant points regarding the later stages is the 

 assumption of the adult condition of the air-sacs and the further 

 development of the recurrent bronchi. These matters are dealt 

 with in section 3. 



The examination of the series of figures described above shows 

 that the external anatomical landmarks of the embryonic lung 

 consist chiefly of its size, shape, the emergence of the embryonic 

 air-sacs, the development of the trunks of recurrent bronchi and 

 the superficial distribution of blood vessels. 



The more important internal features embrace the develop- 

 ment of the bronchial tree, including the in trapulmonary parts of 

 the recurrent bronchi, and the development of air capillaries 

 around the parabronchi. These matters will now receive con- 

 sideration. 



