14 The Development of the Lungs 
bronchus and not an accessory bronchus in the sense of Aeby. In the 
case of the other so-called accessory bronchi, however, this author is in 
accordance with the views of the latter. Robinson, 89, studied the de- 
velopment of the lungs in rats and mice, and finds about the eighth day 
the primitive lung sacs growing lateralwards and dorsalwards, forming 
the bud-like projections into the ccelom from which the primitive and 
stem bronchi arise. The eparterial bronchus, according to Robinson, arises 
as the first division of the right lung bud. As a distinct branch, it is 
absent on the left side, although it is compensated for by a branch of the 
first lateral hyparterial bronchus, which is totally unrepresented on the 
right side and passes up to the apex of the lung. Robinson, in this 
view, 1s in accord with the findings of His. He believes the growth of 
the tree occurs by a flattening of the terminal bud opposite the axis of 
the bronchus and a subsequent division into two unequal segments of 
which the smaller becomes the lateral branch giving rise to what he terms 
an unequal or sympodial dichotomy. Robinson also describes branches 
arising as hollow buds from the main bronchus after it has resumed its 
cylindrical form, allowing the interpolation of secondary bronchi between 
those already existing, while the dorsal accessory bronchi of Aeby arise, 
according to Robinson, by a division of the primary dorsal bronchi, not 
by budding but by having the dorsal stalk split from the point of origin 
of the first median bud as far back as the stem bronchus, allowing this 
medial bronchus to obtain a secondary origin from the stem bronchus 
itself instead of from the primitive dorsal branch. The bronchus infra- 
cardiacus is ontogenetically a derivative of the main stem bronchus, but 
phylogenetically it is, as Aeby suggests, an original branch of the Ist 
hyparterial bronchus. 
With the exception of the Bronchus cardiacus, Robinson has nothing 
to say concerning the ventro-accessory bronchi of Aeby. He calls them 
ventral bronchi, but it is not clear whether either ontogenetically or phylo- 
genetically, as in the case of the most prominent one of the group, he 
considers them accessory branches of his lateral bronchi. 
Ewart, 89, published a large monograph containing a criticism of 
Aeby’s ideas on the architecture of the lungs. Ewart, like Aeby, used 
material consisting of dissections and corrosions of the adult lung, but 
only of one species, namely, man. Apparently this author did not per- 
ceive as clearly as Aeby that the hyparterial and eparterial theory was 
in reality a working hypothesis, which could only receive from embryo- 
logical investigations the evidence necessary for its final substantiation 
or disproof. From his investigations Ewart believes that dichotomy, 
more or less equal, is the principle governing the division of the bronchi 
