40 WILLIAM A. LOCY AXD OLOF LARSELL 



tions are more at variance with previous results than on any 

 other point. The method of development of this sac is very re- 

 markable. In late embryonic stage, as in the adult, it is an un- 

 paired medial sac but it arises from four separate moieties, two 

 from each lung. The lateral moiety springing from the transverse 

 branch of the first entobronchus and the mesial moiety coming 

 (with the exception noted above) from the third entobronchus. 



The chief anticipation of the simultaneous existence of lateral 

 and mesial moieties of this sac is found in Selenka's sketch of two 

 separate sacs on the right lung (see reproduction of the sketch in 

 figure 191 of Lilhe's development of the chick. He says that the 

 sac which we have designated the mesial moiety later unites with 

 the cellula axillaris. Only one moiety of the interclavicular (the 

 lateral moiety) is sketched on the opposite side. As indicated 

 above his sketch of the mesial moiety shows its origin on the 

 wrong side of the bronchus. 



On account of its position on the lung, the lateral moiety is 

 the one that has usually been sketched in the published drawings 

 ■of embryonic stages of the lung and the mesial moiety has com- 

 monly escaped notice. However, when the moieties have united, 

 as in late embryonic stages and after hatching, the more obvious 

 opening of the interclavicular, which is the mesial, has been 

 correctly identified and that part of the sac that is derived from 

 the lateral moieties has been regarded merely as an extension of 

 the mesial moieties. Thus Juillet's diagram of the lung of the 

 embryonic chick represents only the mesial moiety and this as 

 expanded and bearing recurrent bronchi on its lateral border. 

 It is only by following the embryonic development from the 

 eleventh to the sixteenth days that the complex relations of this 

 sac are cleared up. 



Guido Fischer ('05) maintains that the lateral branch of the 

 first entobronchus of the adult opens into the interclavicular sac. 

 He gives a figure of a plastic cast to show this but does not name 

 the bird in which it is found. While Campana does not mention 

 it, his figure 11 is suggestive in showing the termination of the 

 branch in question close to the lateral orifices of the interclavicular 

 sac. 



