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WILLIAM A. LOCY AND OLOF LARSELL 



then enlarges and bends caudally, descending on the mesial side 

 of the central lung tube so that the expanded distal end lies at 

 the side of the main bronchus, not above it, as is the case with 

 entobronchi numbers 1, 2. 



Figures 30, 32 and 33 represent the beginning of a bud project- 

 ing ventrally from the third entobronchus which is to play an 

 important part in the later history of the lung. This hollow bud 



Fig. 38 Dorso-mesial view of right lung of an embiyo slightly younger than 

 the one sketched in figures 34 to 37. Illustrates the exceptional position of ori- 

 gin of the mesial moiety of the interclavicular air-sac, from the second instead of 

 the third entobronchus. 



gives rise to two branches, one cephalad and the other ventrad. 

 The more cephalad branch forms the mesial moiety of the inter- 

 clavicular air-sac (figs. 33 34); the ventrad, bladder-like portion, 

 differentiates into the anterior intermediate air-sac. By the 

 close of the eighth day of incubation both these air-sacs project 

 beyond the boundary of the lung. 



It should be noted that under the exception indicated above, 

 namely, when the second entobronchus gives rise to the mesial 



