189 
The following table of average measurements was obtained from 
12—24 measurements of the different parts: 
Long Short 
Diameter Diameter 
Terminal Bronchus . 0,398 — — 
Millimeters 
Vestibule 27%... “0,196 — = 
Aurium.f. 3. . 0885 0,345 0,225 
Sac-passage . . . 0,143 — — 
Krank |. Lo 6412 0,511 0,313 
Rielle EN. . 615 0,121 0,106 
Bronchial Rir-cell . 0,047 — — 
Blood-vessels. 
The pulmonary artery follows the bronchus closely throughout its 
entire length and when it reaches the last forked division of the 
bronchus it penetrates the lobule until it reaches a point beyond the 
terminal bronchus. Here it divides quite abruptly into as many 
branches as there are atria (fig. 3). None of these arteries seem to 
come directly to the surface of the pleura, and as a rule, no artery 
passes to the periphery of the lobule. The air-sacs lying within the 
proximal portion of the lung lobule receive a separate supply; small 
branches are given off just before the artery penetrates the lobule 
and pass directly to these sacs. Within the lobule the artery spreads 
out on the central side of the air-sac. The capillary net-work arises 
from this*and extending itself over all the air-cells collects on the 
_peripheral side into the veins. 
The pulmonary veins arise from the capillary net-work of the air- 
sac. The artery, bronchus and vein do not lie side by side in the 
lung. It is only at the hilus that they occupy this position. As we 
have already seen the artery accompanies the bronchus, but the vein 
keeps as far away from the bronchus and artery as possible. The 
course of the vein in the lobule is such that we have a vein for each 
air-sac and this vein has a direction at right angles to that of the 
artery. The veins keep on the periphery of the lobule, except in 
a few instances when they send branches between the air-sacs. These 
branches collect the blood from the capillary net-works for the atria. 
Lying between the pulmonary artery and vein we have the richest 
capillary net-work in the whole body. This net-work is much coarser, 
and the capillaries are wider just beneath the pleura than it is in the 
deeper portions of the lung. From the last branches of the artery 
which run between the air-cells this capillary net-work takes its origin 
and spreads out on either side. It forms the greater portion of the 
