276 HERBERT G. WILLSON 
manner in which the infundibula fit in with one another may be 
obtained from figure 4, which is a photograph of the pleural sur- 
face of the model of child’s lung. The numbers on the infundib- 
ula correspond with those on the branchings shown in figure 3. 
From the diagram and the accompanying photographs it 
will be evident that the models reveal no definite space which 
corresponds to Miller’s atrium. Careful study of the models 
shows, it is true, enlargements of the respiratory bronchioles 
where several infundibula communicate with them, but these 
enlargements exhibit no definite delimitation from the remaining 
portions of the bronchioles, and they never assume a spherical 
form. Schulze was probably correct in his contention that a 
special name is not needed for that part of a branch from which 
a number of subordinate branches arise. 
It is interesting to note that Justesen’s description of the 
branchings of a respiratory bronchiole applies very closely to the 
branchings revealed by the models, except in regard to the atrium. 
Both Waters and Justesen held very decided views as to the 
planes in which successive branchings occur. Waters believed 
the plane of two diverging branches to be always at right angles 
to the plane of the two branches preceding. Justesen claims 
that ‘‘there is a strong tendency of the dichotomous divisions 
to lie in alternating planes cutting one another at right angles,” 
but this was not universal. Examination of the models indi- 
cates that Waters’ rule is by no means constantly true. Four 
angles which, according to Waters’ rule, would be 90°, were found 
to be approximately 85°, 90°, 10°, bat 45°. 
The number of biatdlintes that intervene between a non- 
respiratory bronchiole and an air-sac was determined in seven 
cases, and in three the air-sacs were reached at the fifth division, 
in three at the sixth, and in one ease at the seventh. Ogawa 
found from two to nine ramifications, with an average from four- 
teen cases of 5.57. Laguesse found six or seven branchings. 
The alveoli or air-cells on seven different air-sacs were counted, 
the numbers being as follows: 22, 14, 16, 18, 12, 16, and 20, 
giving an average of 16.8. Ogawa’s average is 11. However, 
many of the air-sacs, as Justesen says, are bifurcated or deeply 
