12 



WILLIAM A. LOCY AND OLOF LARSELL 



shown as well as the single orifice by which they open into the 

 lung. 



The lateral moiety of the interclavicular is relatively larger 

 than in earlier stages but otherwise shows no marked change. 



Between the twelfth and fifteenth days' occur relatively rapid 

 expansions of the moieties of the interclavicular sac. The me- 

 sial moieties have fused with each other along the median line 



Fig. 49 xAiiterior intermediate air-sac of the left lung of an embryo, nine and 

 one-half days incubation. (A) View upon the surface that is in contact with the 

 lung. Notable for showing the primordia of the recurrent bronchi springing from 

 the anterior intermediate air-sac The mesial moiety of the interclavicular air- 

 sac is also shown. Ent. 3, opening into the third entobronchus; Bd., buds of re- 

 current bronchi; Mes.moi., mesial moiety of the anterior intermediate air-sac. 

 (B) the same as seen from the cephalic end. Illustrates the connection between 

 the anterior intermed ate and the mesial moiety of the interclavicular air-sacs, 

 and also the forked extremity of the mesial moietv. 



between the two lungs. They have apparently also united with 

 the greatly expanded lateral moieties of the interclavicular (fig. 

 51). The dividing membranes remain for several days subse- 

 quent to the fusion of these different parts. The wall between 

 the mesial moieties does not disappear until the first day after 

 hatching. The septum between the mesial and lateral moieties 

 is less persistent and, so far as dissections indicate, breaks down 

 during the eighteenth day. In attempting to designate the time 



