106 The Development of the Lungs 
by monopody we understand lateral outgrowths from the wall of the 
bronchus whether they occur on the side of or above the terminal bud, 
and by dichotomy we understand an undoubted division of the terminal 
bud. In equal dichotomy the two divisions grow for a time equally but 
later may give rise to a system of monopodial appearance by the selec- 
tion of one branch to continue as the stem, while in unequal dichotomy 
the two buds develop unequally from the first. In the case of dichoto- 
mous divisions, however, it is obvious the portion of the stem between 
two side branches is genetically equivalent to the side branch of the 
lower order. 
Since one can explain theoretically the entire bronchial tree equally 
well by either a monopodial or a dichotomous process of growth, it is 
not surprising to find different views among those who have studied only 
the finished bronchial system. This is well shown among modern in- 
vestigators in the work of Aeby, 80, and Ewart, 89, the former of whom 
believed in monopodial growth from first to last, while the latter says 
“ Dichotomy is the alpha and omega of bronchial division.” Hunting- 
ton, 98, also in working upon comparative material of adult stages finds 
a double system primarily dichotomous with a subsequent monopodial 
type of branching in the development of the stem bronchus. In a sys- 
tem thus capable of two explanations, obviously, the only observations 
which will really aid in solving the question come from those who have 
studied the lungs during the process of their growth. 
If we turn to this series of investigations we find Kiittner, 76, stating 
that “Das Wachsen ist monopodisch, d. h. das Epithelrohr wachst an 
seinem Scheitel ungetheilt fort, wihrend seitliche Sprossen am Stamm 
desselben hervortreten und mit ihrer Lingsaxe zu der des erzeugenden 
Furthermore, he states that these 
buds grow and divide rapidly, giving rise to so many more lateral 
branches than the principal axis that it is difficult in the adult tree to 
39 
Rohres rechtwinkelig gestellt sind. 
recognize its primitive monopodial character. 
Cadiat, 77, describes the process as follows, and it is important to 
remember he is speaking of solid buds: “Il est facile de comprendre 
maintenant comment se produisent les ramifications bronchiques. Un 
premier bourgeon se forme plein et se développe en longueur, l’ampoule 
se produit a Vextrémité. Alors son evolution est arrétée; sur les parois 
naissent des bourgeons secondaires qui se terminent de méme, et ainsi 
les canaux bronchiques vont sans cesse en se multiphant, mais toujours 
dans des directions différentes.” 
Stieda, 78, states: ‘“ Zuerst ist der Canal einfach, dann theilt er sich 
