80 The Microscopie Structure ee 
distinguish the capillary vessels, by which this network is formed, 
from those which connect the blood-vessels, I have called them in 
my former paper on this subject “biliary tubules.” There is no 
apparent difference in the character of both sets of capillaries ; if 
there be any, it is in their diameter, which, however, is a difficult 
matter to determine when the vessels are distended by artificial 
injection. In thin transparent sections of injected human liver, the 
diameter of the biliary tubules is sometimes as large as that of the 
capillaries of the blood, but in the average it appears to be rather 
less. Finding the capillaries in small prepared fragments of fresh 
liver varying in diameter, I am rather inclined in comparing them 
with those of injected specimens to consider the smaller ones as 
belonging to the biliary network.* 
By the union of the smallest branches of the hepatic duct, ori- 
ginating in the network of biliary tubules, the lobular ducts are 
formed. These, by joining each other, form the inter-lobular ducts ; 
which, in their turn, contribute to the formation of still larger ones. 
In this manner the junction of ducts is repeated until, finally, the 
common hepatic duct is formed. 
The walls of the hepatic ducts consist of three coats. The ex- 
ternal coat in which the small arteries and veins ramify consists of 
a loose areolar tissue. The middle one is composed of a similar 
tissue, with the exception of being denser, and containmg some 
smooth muscular fibres; it also lodges some of the hepatic glands 
and a vascular network, similar to that in the external coat of the 
blood-vessels. The internal coat is a mucous membrane. The inner 
side of this membrane, especially in the main hepatic duct and its 
larger branches, is provided with a great number of small oval or 
round pouches, or “ cul de sacs,” as the French would term them. 
They vary in length from ;!5 to +45 of an inch, and are from ;'5 to 
st, of an inch wide. Their lower margin is formed by a crescentic 
fold of mucous membrane, overlapping the sac to some extent. The 
* Tn my article on the “ Hepatic Lobule,” published in the ‘ American Journal 
of Medical Sciences) Jan., 1859, I have stated the diameter of the “ biliary tu- 
bules” to be =,4,, of aninch. Although this statement was true according to 
the extent of my knowledge and judgment at that time, my subsequent researches 
have nevertheless shown me that I had been deceived by appearances. The ele- 
ments which I took to be “biliary tubules,” in my examinations of fragments of 
fresh uninjected liver, and which I represented in the drawing accordingly 
(Figs. 10, 11, 12, and 13), I suppose now to have been capillaries, put on the 
stretch by the needles during the dissection ; or, as the specimens were taken 
from the liver of the hog, they might have been, at least in Fig. 13, fibrils of 
fibrous tissue. In Figs. 1 and 2, drawings taken from injected specimens, the dif- 
ference in the diameters of the “ biliary tubules” and the capillaries of the blood 
may be attributed to the latter having been more perfectly filled with the injecting 
material than the former, though to some extent it is the fault of the engraver, 
for the difference in the original drawing is not as great as represented in the 
engraving. In Fig. 3 the “biliary tubules” alone are injected, and, in conse- 
quence, the diameter is correct. 
