176 
A similar arrangement is seen upon the visceral 
surface of the liver in the Llama. 
- The gall-bladder is absent in all invertebrata, 
the efferent ducts of the biliary organ termina- 
ting for the most part by several openings in 
the digestive stomach. In Fishes the gall- 
bladder is observed for the first time in the 
animal series, but it is not by any means con- 
Stant in its existence. It is absent in many 
genera, and in these cases is frequently re- 
placed by a dilatation upon the hepatic duct 
and by several efferent tubes. In the class 
Reptilia it is invariably ae and _ varies 
considerably in form, in the different genera. 
In serpents it is placed at the extremity or 
even beyond the liver, and occupies the space 
formed by the pyloric contraction of the sto- 
mach. The cystic duct is consequently ex- 
tremely long. Among the Chelonia the gall- 
bladder is enclosed within the substance of the 
liver, and receives its secretion through the 
medium of cyst-hepatic ducts. Some of these 
ducts unite also with the cystic duct and con- 
stitute a ductus communis choledochus. In 
Birds the gall-bladder is occasionally absent, 
as in Pigeons, Toucans, &c. without supplying 
to the comparative anatomist a sufficient reason 
for the peculiarity; being present and absent 
in the same natural genera and under precisely 
the same circumstances of food and climate. 
The bile is brought from the liver by two ducts, 
a cyst-hepatic duct which opens into the gall- 
bladder, and an hepatic duct which terminates 
in the duodenum near to the cystic duct. 
When the gall-bladder is absent, both hepatic 
ducts terminate in the duodenum. There is no 
instance in the whole class of a ductus com- 
munis choledochus. In Mammalia, the gall- 
bladder is by no means constant; it is deficient 
as a general rule, to which there are several 
exceptions, in herbivorous animals, as in the 
horse, stag, elephant, peccary, tapir, whilst it 
is present in the ox, sheep, goat, antelope, &c. 
In the first giraffe examined in this country by 
Owen it was absent; in the next he found two. 
Upon the hepatic duct in the elephant, near to 
the duodenum, there is a remarkable dilata- 
tion. In the cat and seal the ductus communis 
choledochus is dilated in the same situation. It 
is not uncommon to find a double gall-bladder 
or two gall-bladders in the cat; in the kinkaju 
this is supposed to be the normal condition ; 
on in the Museum of the Royal College of 
urgeons there is a preparation, preserved b 
Hunter, of the liver A a seiaeal in whic 
are three gall-bladders. 
Throughout Invertebrata the bile is secreted 
from arterial blood. In Fishes the portal vein 
is formed by veins returning from the tail and 
occasionally from the air-bladder and genital 
organs. In Reptiles a part of the blood from 
the lower extremities unites with that from the 
alimentary canal to constitute the portal circu- 
lation. In Birds the portal vein also receives 
a part of its blood from the tail and lower 
extremities by means of its communication 
with the pelvic veins. ( Fig. 171, u, v, z, page 
338, vol. i.) Injections of the portal vein 
carefully conducted, as well as injections from 
NORMAL ANATOMY OF THE LIVER. 
the internal iliac vein, have shewn that a venc 
communication subsists between the small 
branches of the two systems in the e in- 
testines, even in man. In su 
communication Miiller, in his Ph 
uotes the observations of Retzius: 
essor Retzius, of Stockholm, however, has it 
formed me that he has discovered in man so 
minute communications between the veins 
the intestines and the branches of the ve 
cava. When he injected the vena cava and 
pores with fine injection of different color 
é found that the whole meso-colon and co 
sinistrum were injected with both colours, a 
veins belonging to the two systems at seve 
places formed anastomoses. The veins of 
colon and meso-colon, which belonged to tl 
system of the vena cava and entered the 
renal vein, lay superficially, while those wh 
belonged to the vena porte lay for the mo: 
part nearer the mucous membrane. The € 
ternal surface of the duodenum also had 
ceived injection from the vena cava. 
Breschet too has filled the inferior mesente 
vein from branches of the inferior cava, a 
Schlemm has discovered distinct ce 
munications of the inferior mesenteric ve 
with branches of the inferior cava about t 
anus.” Besides these communications bt 
tween the two systems occurring in the pelvis 
Kiernan points to another most important com 
munication upon the surface of the liy 
“ The capsular veins,” he says, “ are branch 
of the portal vein; these vessels communicat 
freely with branches of the phrenic veins. | 
some cases of atrophy of the liver, and 
cases in which the circulation through the live 
has been for some time obstructed, a collater 
circulation is established by means of th 
communications which take place between t 
capsular branches of the hepatic artery 
portal vein and those of the hans artery and 
vein.” In diving animals, as in the otter an & 
seal, in which large venous reservoirs exis 
upon the inferior cava, for collecting the re- 
turning blood during submersion, the hepatic 
veins are muscular. Kiernan observes with 
regard to the hepatic veins of the seal that they 
“differ in many respects from those of any 
other animal I have examined. The intra- 
lobular veins at their exit from the lobules do 
not as in other animals terminate immediately 
in the hepatic veins: these vessels enter the 
hepatic venous canals, where they unite into 
branches, which, like the vaginal branches of 
the portal vein, are connected by a fine cellular 
tissue, with which they form around the he- 
patic veins a cellulo-vascular sheath precisely 
similar to that surrounding the branches of the — 
portal vein. i 
Vee : 
1010 
“« py, 
vo. 
The structure of the two sheaths 
is similar, but their uses are different. That 
of Glisson’s capsule has been explained; 
the capsule of the hepatic veins in the seal 
appears destined to admit of the muscular con- — 
tractions of these vessels.” “ The external 
coat of the hepatic veins is composed of cireu- 
lar fibres which in the larger vessels form a 
complete tunic. In the smaller vessels the — 
fibres are arranged in the form of circular fas- 
