THE SPLEEN 439 
portal canals of the interlobular tissue. The branches of the portal vein (Venwe 
interlobulares) give off intralobular branches which form plexuses of capillaries in 
the lobules and give rise to a central vein (Vena centralis). The interlobular 
branches of the hepatic artery (Rami arteriosi interlobulares) are of relatively 
small size. They supply mainly (if not exclusively) the interlobular tissue, the 
capsule, and the walls of the vessels and ducts. The hepatic veins! (Venz hepatic) 
empty into the posterior vena cava as it lies in the fossa of the gland. Their 
ultimate radicles are the central lobular veins (Ven centrales), which emerge from 
the bases of the lobules and join 
the sublobular veins (Ven sub- 
lobulares); the latter unite to form 
the hepatic veins. The largest 
hepatic veins, three or four in 
number, join the posterior vena 
cava just before it leaves the liver 
to pass through the diaphragm. 
The nerves come from the 
hepatic plexus, which is composed 
of branches from the vagus and 
sympathetic nerves. 
THE SPLEEN 
The spleen (Lien) is the 
largest of the heterogeneous group 
of organs which are usually desig- 
nated ductless glands.” It is situ- 
ated chiefly in the left parachon- 
driac region, in close relation to the 
left part of the great curvature of 
the stomach, to which its long axis 
corresponds. Its size and weight 
vary greatly in different subjects, 
and also in the same subject under 
different conditions, depending 
chiefly on the great variability of 
the amount of blood contained in 
it. The average weight is about 35 
to 40 ounces (ca. 1 kg.), its length a, Dorsal extremity or base; b, c, anterior and posterior basal 
about 20 inches (ca. 50 em.), and angles; d, anterior border; e, ventral extremity or apex; 1, 2, 3, 
its greatest width about 8 to 10 impressions of last three ribs. 
inches (ca. 20 to 25 cm.). It is 
usually bluish-red or somewhat purple in color. In the natural state it is soft and 
yielding, but not friable. 
Fic. 375.—SPLEEN OF Horse; PARIETAL SURFACE. 
The weight, which is extremely variable, appears to range ordinarily from about one to eight 
pounds, although the latter figure even may be exceeded without any apparent evidence of disease. 
_ ‘The hepatic veins may be recognized on section from the fact that they remain open, 
being connected closely with the parenchyma. 
_ *The ductless glands are organs which elaborate substances that pass directly into the 
veins or lymphatics, instead of being conveyed away by ducts. This process is termed internal 
secretion. The ductless glands include the lymph glands, which are described with the organs 
of circulation; the thyroid and thymus bodies, described usually with the respiratory organs; 
the adrenal or suprarenal bodies, described with the urinary organs; the pineal and pituitary 
bodies, described with the brain; and the spleen, described with the digestive system as a matter 
of convenience. The spleen is not, strictly speaking, a gland at all: it is not epithelial in origin 
or structure, but is mesenchymatous. 
