THE EMBRYOLOGY OF THE BIRD's LUNG 491 



make a sharp bend caudally and their distal extremities extend 

 to the lateral border of the lung. Just before reaching this 

 wall, the second latero-bronchous bifurcates, and later forms a 

 number of divisions which result in supplying the middle part of 

 ventro-lateral lung region with parabronchi (figs. 39 and 40). 



The third laterobronchus does not divide like the second, })ut 

 projects beyond the lung wall and forms the primordium of the 

 posterior intermediate air-sac (figs. 39 and 40). This sac makes 

 its appearance at the beginning of the ninth day. 



Campana says that this a'.r-sac arises on the second latero- 

 bronchus, but he did not study development and a correct un- 

 derstanding is possible only by following embryonic stages. 



A number of branches are later given off, from the third latero- 

 bronchus between the air-sac and the point of connection of the 

 laterobronchus with the mesobronchus. The first branches of 

 this kind appear on the tenth day and the others later. These 

 branches which extend ventro-laterally, must not be confused 

 with the dorsally and forward projecting buds from the air-sac 

 itself (fig. 40). These latter are the recurrent bronchi and will 

 receive separate consideration on a following page. 



We may now consider the first laterobronchus — so-called be- 

 cause it is the most anteriorly situated, although arising later. 

 It is first distinguishable on the second half of the seventh day 

 as a boss-like bud from the antero-lateral wall of the embryonic 

 vestibulum (fig. 32, Lat. 1). It grows forward a short distance 

 and then turns ventral (fig. 34). Later a number of branches 

 are given off its anterior and lateral surfaces which produce short 

 parabronchi that eventually anastomose with the deep-lying 

 branches of the transverse branch of the first entobronchus and 

 with parabronchi of the dorsal ramus of the second entobronchus. 



The side branches of this laterobronchus anastomose also to 

 some extent with the anterior tips of the recurrent bronchi of 

 the abdominal air-sac. 



Laterobronchi numbers four and five take their origin from the 

 posterior division of the mesobronchus, just caudad to the ex- 

 panded part or embryonic vestibulum. They appear during the 

 eighth day of incubation, and at the beginning of the ninth day 



