326 CHIKANOSUKE OGAWA 
branches there may remain but one. Referring to figure 6, 
one may gain a clear conception of this matter. According to 
Miller, two to five air-sacs are sent off from the atrium. Justesen 
states that in the 80-cem. ox embryo four air-sacs and in the adult 
three air-sacs are sent off from the atrium. The number of 
alveoli contained in one air-sac is estimated to be from 10 to 
20 by Rossignol. My calculation is as follows: 
The number of alveoli 5, 8, 9, 10, 11, 13,16, 195,26, 
a Ga Lee 
The number ‘of times’ "5, 1,3, 19a) 2, 2, 288 
ATRIUM 
Since Miller proposed the name atrium, in nomenclature, for 
the new aspect he found in the respiratory tubes of the dog 
lung by means of wax-plate reconstruction, many authors have 
been discussing it without coming to a common understanding. 
I will first briefly quote Miller’s statements: 
Between each air-sac and terminal bronchus there is a cavity, con- 
stant in all portions of the lung, which I shall term, atrium. The 
terminal bronchus is made up of smooth muscle fibers, lined with 
cylindrical epithelial cells, from the tip of the terminal bronchus three 
to six vestibules arise. (Vestibules can be used interchangeably with 
atrium because he withdrew the term vestibule in a later publication.) 
The diameter of the atrium is slightly more than half that of the air-sac 
and unlike it each atrium has three or more openings. ‘These open- 
ings communicate on the one hand with the air-sacs and on the other 
with the terminal bronchus. 
Since Miller’s so-called terminal bronchus is lined by cylin- 
drical epithelial cells, it ought to be the part of the bronchial 
tube above the bronchiolus respiratorius, but according to his 
later publications it is said to be equivalent to the alveolar ducts. 
The fact that authors understand the term atrium in different 
ways may be due to this inaccurate description. Now Bohm- 
Davidoff, Spalteholz, Jordan-Ferguson, Morris, Piersol, Shafer, 
and others adopt this term in their text-books, and Gray con- 
siders it the same as an alveolar duct. V. Ebner in a way 
opposes this, as the term atrium has no histological significance 
and arouses only confusion in terminology. Oppel opposing 
