485 



Early on the ninth day of incubation carefully prepared air in- 

 jections show many important advances. The primordia of all five 

 air-sacs (Fig. 2, pr., s.l, a J, p.i^ ah.) now project beyond the lung 

 surface. 



The prebronchial sac (Fig. 2, pr.) is the forward prolongation of 

 the more dorsal lobe of the first entobronchus. From the ventral- 

 most tip of the same entobronchus may now be seen a forward pro- 

 jecting bud (s.2) which does not yet extend beyond the lung wall. 

 This bud is the foreshadowing of the second or lateral moiety of the 

 sub-bronchial sac, for, as is shown in subsequent development, this 

 bud fuses with the mesial moiety (s.l) from the third entobronchus 



Fig. 2. Fig. 3. 



Fig. 2. Lateral aspect of the right lung of chick embryo of the early ninth 

 day stage, aft., abdominal air-sac, with bud of recurrent bronchi, {r.br.)\ a.i., anterior 

 intermediate air-sac with three papilla-like buds (r. 6r.) of the recurrent bronchi; 

 br.. bronchus; d.r. dorsal ramus of second entobronchus; ec, ectobronchi; p.i., post- 

 erior intermediate air-sac; pr., prebronchial air-sac; S.l, mesial moiety of sub- 

 bronchial air-sac from the third entobronchus; S.2, lateral moiety of sub-bronchial 

 air-sac. Camera sketch. X 43. 



Fig. 3. Dorso-mesial view of a slightly earlier stage than is shown in fig. 2. 

 illustrating the mesial moiety (S.l) of the sub-bronchial air-sac arising in an exceptional 

 position from the second, instead of from the third entobronchus. ab., abdominal; 

 a.i., anterior intermediate air-sac; fer., bronchus; en.3, third entobronchus; pr., pre- 

 bronchial air-sac; S.l, mesial moiety of subbronchial air-sac. Camera. X 43. 



to form the so-called sub-bronchial air-sac. The mesial moiety is 

 well developed at this stage. 



The ramus (r.l) of the third entobronchus to which attention 

 Avas called in Figure 1 bifurcates early in the seventh day of in- 

 cubation (not figured). The smaller and more anterior branch resul- 



