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NORMAL ANATOMY OF THE LIVER. 
ciculi, which are connected with each other 
by oblique intermediate fibres. All the fas- 
ciculi do not extend completely round the 
veins ; some, dividing into two portions, unite 
with fibres from those above and below, and 
form other fasciculi.” “ In the porpoise the 
hepatic veins are connected to their canals; 
no circular fibres are seen in their coats. Their 
external surface is reticulated, the ridges cor- 
responding to the interlobular fissures, where 
the interlobular cellular tissue is continuous 
with the cellular coat of the veins. The mouth 
of an intra-lobular vein occupies the centre of 
each space circumscribed by the ridges.” 
The distribution of the vessels in the liver 
in the three great classes, Reptilia, Aves, and 
Mammalia, has been ascertained to be the same 
with that which has been so completely illus- 
trated in the discoveries of Kiernan. In 
Fishes but few observations have been made, 
but analogy would lead us to infer that the ge- 
neral arrangement must be the same. 
Development of the liver in the embryo.— 
The development of the liver in the embryo 
commences so early in Mammiferous animals, 
hurries so rapidly through its different phases, 
and is completed so soon, that it has hitherto 
been impossible to obtain any connected and 
recise information with regard to its progress. 
he observations of eminent physiologists made 
from time to time have, however, shewn that 
the mode of its development is in all respects 
similar to the development of the liver in the 
chick. Indeed, the egg of the bird is in the 
highest degree favourable to anatomical exa- 
mination, both on account of its large size and 
the facility with which the incubated egg may 
be obtained from hour to hour, and from day 
to day. The principle of development there- 
fore being the same in the ovum of the bird as 
in Mammifera, I shall here trace the progress 
of the liver in the chick according to the most 
recent researches of Baer. 
In the embryo of the fowl at the commence- 
ment of the third day, the common vein of the 
body is embraced by two pyramidal cecal 
pouches which communicate by their bases 
with the intestinal canal, and which shoot for- 
wards so as to carry before them a fold of the 
vascular layer of the germinal membrane, in 
which they begin to ramify by giving off cecal 
branches from their sides and extremities. 
These two cecal tubuli with their correspond- 
ing ramifications form two flattened processes, 
which represent the two lateral lobes of the 
liver. By the end of the third day the two 
processes resemble -folds of the vascular layer 
in which the tubuli are seen ramifying; they 
have increased in size and almost surround the 
vein. On the fourth day the liver has the appear- 
ance of two flattened processes which enclose 
the vena porte. The hepatic tubuli have be- 
come lengthened and further removed from the 
intestine, and have ramified more freely in the 
vascular layer. By their bases the hepatic 
tubuli approach nearer to each other, and at 
the end of the fourth day they coalesce and 
form a common tube. On the fifth day the 
liver has attained considerable size; its two 
VOL. III. 
177 
lobes have become thick and appear to possess 
a spongy texture in their interior. The hepatic 
ducts are connected with the intestine by a 
common duct, the ductus communis chole- 
dochus ; and the portal vein gives off large 
branches which are distributed among the ra- 
mifications of the ducts. On the sixth and 
seventh days the liver receives an abundance 
of blood and is nearly as red as the auricle of 
the heart. The left lobe is sensibly smaller 
than the right. On the eighth>ninth, and 
tenth days the liver has lost its great redness 
and presents a yellowish brown tint; the vessels 
have diminished in calibre, while the paren- 
chyma has increased, and the gall-bladder has 
become apparent. The succeeding days aug- 
ment the size of the organ, and mould it to 
the form which it possesses after the escape of 
the chick from the egg; it begins to secrete 
bile; and the gall-bladder assumes the pyri- 
form shape which it retains in after-life. 
In the human ovum the formation of the 
embryo commences visibly at about the third 
week of intra-uterine existence; the parietes 
which separate the embryo from the ovum begin 
to be developed, and rudiments of the intestinal 
canal, the liver, and the heart soon become 
distinctly visible. Upon its earliest appearance 
the liver is of large size, and between the third 
and the fifth week is one-half the weight of 
the entire body, divided into several lobes of 
a reddish grey colour, and receives a large pro- 
portion of blood from the omphalo-mesenteric 
vein. From the fifth to the eighth week the 
liver extends as low as the margin of the 
pelvis; it is soft, almost pulpy, and greyish in 
colour. The gall-bladder is developed in the 
form of a lengthened filiform cord, having an 
extremely minute canal through its centre. By 
the third lunar month the liver extends nearly 
to the pelvis and almost fills the abdomen, and 
the right lobe has increased somewhat beyond 
the left. The texture is more firm and of a 
redder colour, and the gall-bladder is long and 
conical. At the fourth lunar month the liver 
is still prolonged nearly to the margin of the 
pelvis, but the left lobe is evidently shorter 
than the right. The gall-bladder is elongated, 
straight, and vertical in direction, and contains 
a little mucus. Upon its internal surface a 
few ruge begin to be perceived ; it receives no 
bile, although a small quantity of that fluid is 
secreted by the liver and poured into the in- 
testine. By the fifth lunar month the liver has 
acquired an increased consistence and deeper 
colour. It no longer descends so low as the 
pelvis, but appears to have diminished in bulk 
in proportion with the size of the abdomen. 
The gall-bladder assumes a more: horizontal 
direction, and the contained mucus has a yel- 
lowish green tint. The openings of the ductus 
choledochus and pancreatic duct, at first placed 
at a considerable distance from each other, 
approximate and produce less projection of 
the mucous membrane. By the sixth lunar 
month the descent of the liver is still more 
curtailed, the fcetus increases in development 
from before backwards, and the organ becomes 
more horizontal. By the seventh lunar month 
N 
