304 STRUCTURE OF THE LIVER. 
bladder (fig. 168), which serves to retain all the fluid that is _ 
poured forth by the gland during a considerable length of 
a 
time, and thus prevents the necessity for its being continually — 
passed out of the body. 
Characters of Particular Secretions. 
363. In nearly all animals, the Ziver holds the first rank 
among Glands or secreting organs, in regard both to its size 
and to the obvious importance of its function. The principal 
varieties of its plan of structure in the Invertebrated classes — 
having been already noticed (§ 356), we shall here limit 
ourselves to a sketch of that peculiar arrangement of its 
elementary parts, which presents itself in Man and other 
Vertebrata. The position of this organ in the abdominal — 
cavity is shown in fig. 30. It is chiefly composed of a mass 
of cells of a flattened spheroidal form (fig. 169, B), the dia- — 
meter of which is usually from 1-800th to 1-1600th ofan inch ; 
each cell presents a distinct nucleus, which is surrounded by 
yellow biliary matter in a finely granular condition; and in 
the midst of this there are usually one or two large fatty 
globules, or five or six small ones. The quantity of fat in 
tke liver is very liable to increase, however, when there is a 
large amount of oily or fatty matter in the food, or when the 
respiratory function is not performed with sufficient activity. 
The hepatic cells are 
clustered together into 
lobules of irregular form, 
but about the average 
size of a millet-seed;— 
these lobules are disposed 
upon the ramifications of 
the hepatic vein (fig. 
169, a), like leaves upon — 
the branches of a tree; 
and they are separated — 
Fig, 169.—Porriox or rus Human Liver. from one another by the 
A, Showing the manner in which the substance peculiar distribution of § 
of its lobules is disposed around the branches € ” li 
of the hepatic vein a; B, cells of which the the * portal” vessels and 
—_ 
lobules are composed, more highly magnified. of the hepatic ducts. — 
aA 
The Vena Porte, it will be remembered, collects the blood ~ 
that has been distributed to the alimentary canal, and conveys — 
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