404 The Vascular Supply of the Pleura Pulmonalis 
only here and there, have I found branches of the bronchial artery 
passing directly to the pleura. It does not seem to me that this is due 
to faulty injections, for I have always been able to obtain a well-filled 
system of vessels in the pleura. 
I have always found that the branches of the bronchial artery which 
reach the pleura came from the depth of the lung and that they are larger 
in proportion and more branched than in the sheep or in the horse. 
Kiittner (8) has given an excellent illustration in. his Fig. 7 of the 
artery spreading out in the pleura of the lung of an infant. The figures 
which I have obtained in the adult agree with his of the child. 
It appears therefore, that in the sheep and in the horse the type of 
the distribution of the bronchial artery to the pleura is different from 
that in man. In the two former, the supply is mainly direct, in the latter, 
indirect. 
The lymphatics of the pleura in man, like those of the sheep and the 
horse, are surrounded by a network of blood-vessels which is derived 
from the bronchial artery (Fig. 11). This network seems to be finer and 
there are more encircling branches than is the case with either the sheep 
or the horse, though some of my preparations of the sheep’s pleura show 
a very complete network. 
The capillary network into which the bronchial artery breaks up in the 
pleura gives rise to radicles which join the pulmonary vein. These 
venous radicles are larger in the human pleura than in either the sheep 
or the horse (Fig. 12). 
ANASTOMOSES BETWEEN THE BRONCHIAL ARTERY AND THE PULMONARY 
ARTERY. 
The question naturally arises: What constitutes an anastomosis? In 
general, we understand by the term, as applied to the vascular system, a 
communication between two different sets of vessels, as, for example, that 
between the carotis interna and the cerebri posterior ; or between branches 
of the same set of vessels, as, for example, that between the branches 
of the mesenterica superior. In each of these instances we have to do 
with sizable vessels and it is the absence of sizable vessels that plays an 
important rdle in determining what constitutes an “end artery.” An 
example of this differentiation is found in Spalteholz’s study of the 
distribution of the blood-vessels in muscle (14). 
Ruysch (12), Haller (4), Hyrtl (6) and others, say that the anasto- 
mosing branches between the two arterial systems are of sufficient size 
to be seen with the unaided eye. If this be true, an injecting mass con- 
