130 
MAMMALIAN ANATOMY 
mass made up of numerous lobules, each having somewhat the 
form of two frusta of pyramids placed base to base and thus 
appearing in section in irregular polygonal form. Study micro¬ 
scopically, sections of the liver of various mammals (the pig par¬ 
ticularly), for the relation of the lobules to each other and the 
identification of blood vessels and bile ducts shown in a transverse 
section of a lobule as follows:. Running through the center of 
each lobule is a small vein (the intralobular vein) which collects 
the blood from the capillaries of the lobule, while in the connective 
tissue at the angles between lobules (interlobular) are the ultimate 
branches of the hepatic portal vein and the hepatic artery, both 
of which bring the blood to the capillaries of adjoining lobules. 
With these interlobular blood vessels are found the bile ducts 
which convey the bile, the secretion of the liver cells, away from 
the bile capillaries (i.e., lumina of tubules) of the adjoining lobules. 
Note that the veins and arteries may be distinguished from each 
other by the character of their walls, the arteries having the thicker 
walls and the lining thrown into folds. Note also that the 
cuboidal epithelial cells lining the bile ducts distinguish them 
from both veins and arteries. Study sections of injected liver to 
corroborate these points. Draw a cross section of a single lobule, 
showing its relation to adjoining lobules , and the arrangement 
of blood vessels and bile ducts associated with it. 
Under high power study the details of liver cells. Note their 
cuboidal form, nucleus and cytoplasm, the latter often exhibiting 
numerous glycogen granules and other non-living structures. The 
bile capillaries which are really the lumina of the gland tubes which 
make up the liver, are distinguishable here and there merely as 
clefts beween the liver cells; the blood capillaries have their own 
lining of flat endothelial cells, and in injected liver, may be seen 
among the gland cells. (Compare with sections of Amphibian 
and reptilian liver in which the cells are larger and the structure 
simpler. Note particularly that in the reptilian liver the tubular 
character of the gland is very evident.) Draw a few adjoining cells 
showing all the details you can make out. 
