502 WILLIAM A. LOCY AND OLOF LARSELL 



The most significant feature of dorsobronchi is the circular 

 plexus of the dorsal region (reseau anastomotique of Campana) 

 already described. 



As Campana pointed out, in 1875, some bronchi of identical 

 appearance are inserted on the stems of ectobronchi, instead of 

 on the mesobronchus, and this circumstances indicates a transi- 

 tional form between secondary and tertiary bronchi. We have 

 designated as dorsobronchi only those (about twenty-five) that 

 have an orifice communicating directly with the mesobronchus. 



It is to be noted that there are no bronchial stems on the oppo- 

 site (ventral) wall of the mesobronchus. 



A careful study of the intercommunications of the air passages 

 is very convincing that there is a universal anastomosis of para- 

 bronchi, and if there be any blind endings or culs-de-sac in the 

 lungs, they are very exceptional. In our observations we have 

 never been able to find an undoubted blind ending of air pas- 

 sages. This labyrinthine communication extends also to the air- 

 capillaries that radiate around the parabronchi. 



Besides the terminal anastomoses of parabronchi there are fre- 

 quent lateral communications by short canals. This kind of 

 communication is especially well seen on the parabronchi of 

 ento- and ectobronchi (figs. 42 and 43). 



The air capillaries. The ultimate divisions of the bronchial 

 circuits are the air-capillaries that are radially arranged about 

 the parabronchi. It is to be kept in mind tht even these micro- 

 scopic branches do not end in culs-de-sac. 



The lung parenchyma, beginning on the ninth day, becomes 

 arranged around parabronchi into prismatic columns which on 

 cross-section are hexagonal. In the middle of these hexagonal 

 areas lie the circular parabronchi, and in the adult lung a large 

 number of minute branches project radially into the lung paren- 

 chyma. The intercommunicating distal ends of these branches 

 constitute the air-capillaries. 



All these parts arise in succession in the embryo between the 

 fourteenth and the sixteenth day of development. The vesti- 

 bules appear about the fourteenth day as hollow buds projecting 

 from the walls of the parabronchi. They develop into short cyl- 



