Joseph Marshall Flint 
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to the origin of the pulmonary arteries in the embryo above the lungs, 
and states: ‘“ Hin spater eparterieller Bronchus muss somit so lange 
hinter ihr legen, als nicht in Folge des hohern Aufsteigens des Organs 
eine bogenformige Ablenkung derselben tiber den ersten Ventralbronchus 
hinweg nach vorn hin stattgefunden.” While Aeby looked upon the 
lungs instead of the heart as the movable factor in establishing the adult 
relationships of the arteries to the tree, he recognized notwithstanding 
this misinterpretation, the necessity of the embryological topography of 
the “ eparterial ” or first lateral bronchi to produce the conditions which 
we find in later stages. It is clear from the above account of the de- 
velopment of the pulmonary arteries that these delicate vessels which 
regularly follow the growth of the bronchi and do not, in fact, appear 
in any part of the lung until after the respective branches which they 
supply are present, have no formative influence on either the structure 
or relationships of the bronchi, but are simply passive followers of their 
development produced by histomechanical principles from the capillary 
plexus which surrounds them. Finally, a crossing of the stem bronchus 
by the artery does not occur until after birth when all of the bronchi 
are laid down, and even then, in the strict sense of Aeby, does not exist 
as Zumstein and Narath have already shown. It is thus most difficult 
to determine just what led Aeby to lay such stress upon the adult rela- 
tionship of the artery to the stem when he obviously, as the above quota- 
tion shows, clearly recognized that it was not associated with the earlier 
formation of bronchi, but was due, as he supposed, to the later ascent of 
the lungs. Furthermore, the pulmonary artery is not responsible for 
the dorsal and ventral divisions of the stem bronchi as we have ventral 
and medial elements also arising from the stem away from any possible 
influence of the artery. 
Miller, 98, brings forward an interesting suggestion with reference 
to the effect of the pulmonary arteries on the tree dependent upon the 
descent of the heart in mammals which have had the form of their chest 
wall altered by their life in water. The pulmonary arteries, according 
to Miiller, following the descent of the heart tend to drag the “ Ventral 
bronchi” caudalwards, leaving the dorsal bronchi free and uninfluenced 
by the arteries to wander up on the stem bronchus or trachea to form 
the so-called ‘ eparterial” bronchi. This ingenious suggestion is not 
borne out, however, by the facts of embryology, for as we have seen, all 
the bronchi are well formed before the heart in its descent reaches a 
level where the pulmonary arteries could exert such a traction upon the 
lateral bronchi. 
