468 WILLIAM SNOW MILLER 
In the preceding section I have discussed the presence and 
relationship of the atria, sacculi alveolares and alveoli pulmonis. 
It is not necessary, therefore, to enter into a detailed discussion 
of these portions of the lobule. I will only add that Oppel has 
demonstrated the presence of atria in the lungs of a long series 
of vertebrates. Justesen found them in the lung of the ox. 
Councilman has demonstrated them in the human lung and Flint 
in the lung of the pig. I have already given the list of recon- 
structions that I have made; each of which shows well marked 
atria. 
THE LOBULE 
The term ‘lobule,’ as applied to lung structure, is used at the 
present time to designate two different areas. By some it is 
applied to those large areas, faintly marked out on the surface 
of the human lung, but distinctly marked out by broad septa on 
the lung of the ox. By others it is applied to much smaller 
areas which consist of a ductulus alveolaris and the air spaces 
connected with it. Laguesse and d’Hardiviller call the larger 
areas the lobule, and give the name acinus to the structures con- 
nected with the ductulus alveolaris. 
If one review the literature of the lung it will be found that 
almost universally the term lobule is applied to the structures 
connected with the last division of the bronchial tree. Various 
names are given to this last division and to the structures which 
lie beyond it; but, whatever the name, the ensemble forms the 
lobule. These lobules, primary lobules if you so choose to call 
them, are grouped together into secondary lobules and these sec- 
ondary lobules collectively form the lobes. 
The term acinus should be discarded as it is too indefinite. 
In its present usage, as applied to gland structure, it is not used 
consistently. If any part of the lung structure is to be compared 
to an acinus, it is an atrium and its sacculi alveolares; but until 
‘acinus’ is used to describe a more definite portion of a gland 
than its present usage does, nointelligent comparison can be made. 
Elaborating the definition of the lobule as given in connection 
with the air spaces, the complete lobule consists of a ductulus 
