AIR SPACES IN LUNG OF CAT 463 
face while in still other instances it is attached to the free end 
of the cartilage. The bronchial muscle on the other hand is 
always situated between the cartilage and the mucosa. He fur- 
thermore states that the bronchus of the inferor lobe shows the 
same musculature as the trachea, while in the bronchi of the 
middle and upper lobes we have a different muscle. Guieysse 
applies this arrangement of muscle to Aeby’s theory as follows. 
The fact that the musculature of the bronchus of the inferior lobe 
is the same as that of the trachea corresponds to Aeby’s state- 
ment that the bronchus of the lower lobe is a continuation of 
the main bronchus. He also argues that this arrangement of 
muscle has an important bearing on the question of bronchial 
division. If the division were dichotomous the upper and lower 
bronchi ought to be alike in every respect; but this is not the 
case, for while the upper bronchi are soon enveloped in their 
muscle, the lower bronchus retains the tracheal muscle. This 
proves, according to Guieysse, that we are dealing with a con- 
tinuation of the main bronchial trunk. 
Oppel, commenting on the above statements of Guieysse, says 
that caution is necessary in applying his results as arguments 
for monopodial division, for, even if the branching were dichot- 
omous, the peculiar arrangement of the muscle might be a second- 
ary acquisition; on the other hand, it does not seem proven that 
in monopodial branching the upper bronchi should vary, in so far 
as their musculature is concerned, from the lower bronchi or 
the bronchial trunk. 
Of all investigators, Justesen holds most decidedly that the 
method of division in the development of the bronchial tree is 
strictly dichotomous. His conclusions are based upon studies of 
the development of the bronchial tree of the ox. He followed 
carefully the branching of a single bronchiole throughout its en- 
tire course and found that ‘‘each of the side branches is homolo- 
gous in all its branches to the continuation of the trunk.” 
d’Hardiviller emphatically declares that the mode of division 
is monopodial. In his work on the rabbit’s lung he says that 
the end bud remains undivided and that the lateral branches 
originate by no means through true or false dichotomy, but from 
