HUMAN LUNG 319 
ORDER. ANGLE, AND TYPE OF RAMIFICATION 
Alveolar ducts are closely beset by alveoli. Therefore the 
designation ‘wall of the alveolar ducts’ means only the small 
spaces between each alveolar mouth. 
The alveolar ducts divide themselves several times to reach 
the air-sacs. Aecording to Laguesse, there are six or seven 
ramifications before the air-sacs are reached. In my model there 
are four groups of alveolar ducts. I counted the orders into 
which the alveolar ducts divide before reaching the air-sacs as 
follows (I term the ramification of the alveolar duct from the 
respiratory bronchiole the first order): 4, 5, 3, 7, 6, 5, 5, 4, 5, . 
8, 9, 8, 7, 2. Thus in my model there are two to nine ramifi- 
cations. Some air-sacs may very probably branch off directly 
from the respiratory bronchiole and others may pass through nine 
orders of ramification, although no such cases can be found in 
my model (figs. 4, 5, and 6). 
Now the angle of ramification of alveolar ducts is given from 
an acute angle to an angle of 180°, usually from 30° to 50° by 
Schulze and about a right angle by Toldt. In my model the 
angles of ramification are many, ranging from wide angles to 
acute. 
Monopody, dichotomy, and sympody are terms generally 
used to designate the type of ramification of the bronchial tree. 
Much attention has hitherto been given to the type of ramifica- 
tion of the embryonic and adult bronchial tree. In consequence, 
an extensive literature has accumulated; but leaving recapitula- 
tion to Miller, I will here only refer to some accounts concerning 
the ultimate ending of the bronchial tree of the adult lung. 
Merkel seems to recognize both monopody and dichotomy in 
the ultimate ramification. Miiller is of the opinion that the 
mode of division of the terminal air spaces presents no definite 
rule, though dichotomy is very generally present and one may 
observe not infrequent occurrences of unequal branches. Ac- 
cording to Miller, two processes seem to prevail in the lung of 
the cat, } 
