The =liver= (Hepar) is the largest gland in the body. It is situated
obliquely on the abdominal surface of the diaphragm. Its highest point
is at the level of the right kidney, its lowest on the left side,
usually about three or four inches (ca. 8 to 10 cm.) from the abdominal
floor, opposite the lower end of the seventh or eighth rib. The greater
part of it lies to the right of the median plane.
It is red-brown in color and is rather friable. Its average weight is
about ten to twelve pounds (ca. 5 kg.). When in the body, or if hardened
_in situ_, it is strongly curved and accurately adapted to the abdominal
surface of the diaphragm. When removed in the soft state, it flattens
out into a cake-like form quite different from its natural
configuration. It presents for description two surfaces and a
circumference, which may be divided into four borders.
The =parietal surface= (Facies diaphragmatica) is strongly convex, and
lies against the diaphragm. It faces chiefly upward and forward. It
presents, just to the right of the median plane, a sagittal groove for
the posterior vena cava (Fossa venæ cavæ). The vein is partially
embedded in the substance of the gland, and receives the hepatic veins.
The =visceral surface= (Facies visceralis) faces in general downward and
backward; it is concave and irregular, being moulded on the organs which
lie against it. It presents, a little to the right of the median plane,
the =portal fissure= (Porta hepatis). Through this the portal vein,
hepatic artery, and hepatic plexus of nerves enter, and the hepatic duct
and lymph vessels leave the liver. The portal or hepatic lymph glands
are also found here. The pancreas is attached at and to the right of the
fissure, and the gastro-hepatic omentum to the left of it. Above the
fissure is a ridge which represents the caudate lobe (Lobus caudatus
Spigelii), and is continued to the right by the pointed caudate process
(Processus caudatus). Further to the left there is a large depression
(Impressio gastrica) for the stomach. To the right of this may be seen a
groove passing to the right and dorsally; this is the duodenal
impression (Impressio duodenalis). Ventral to these is a large
depression for the great colon (Impressio colica). Dorsal to this is a
smaller depression for the blind end of the base of the cæcum.[98] Coils
of the small intestine may also lie on this surface, and the apex of the
spleen may reach to it when the stomach is empty.
The =dorsal border= (Margo obtusus) is thick for the most part. It
presents from right to left: (1) a depression for the right kidney
(Impressio renalis); (2) a notch, which is the dorsal end of the fossa
venæ cavæ; (3) a deep notch (Impressio œsophagea) which is mainly
occupied by the thick margin of the œsophageal opening of the diaphragm.
The =ventral border= is thin, and is marked by two deep =interlobar
fissures= or =incisures= (Incisuræ interlobares), which partially divide
the organ into three principal =lobes=—=right=, =middle=, and =left=.
The right lobe is the largest, except in old subjects, in which it is
frequently much atrophied. The middle lobe is the smallest. It is marked
by several small fissures, and by the =umbilical fissure= (Incisura
umbilicalis); the latter contains the umbilical vein in the fœtus, which
is transformed into the round ligament after birth.
The =right border= is thin and long. It is nearly vertical, and extends
backward to about the middle of the sixteenth rib.
The =left border= is thin and short. It extends backward to a point
opposite the lower part of the ninth or tenth rib. The ventral and
lateral borders together constitute the margo acutus.
[Illustration:
FIG. 274.—LIVER OF YOUNG HORSE, HARDENED _in situ_, PARIETAL SURFACE.
]
The liver is held in position largely by the pressure of the other
viscera and by its close application to the diaphragm. It has six
ligaments.
1. The =coronary ligament= (Lig. coronarium hepatis) attaches it closely
to the diaphragm. It consists of two laminæ. The right one is attached
to the right of the fossa venæ cavæ; the left one begins to the left of
the vena cava and passes upward and outward, becoming continuous with
the left lateral ligament at the left margin of the œsophageal notch; it
detaches a middle fold which extends to the notch and is continuous with
the small omentum. The two laminæ unite below the vena cava to form the
next ligament.
2. The =falciform ligament= (Lig. falciforme hepatis) is a crescentic
fold which attaches the middle lobe to the sternal part of the diaphragm
and to the abdominal floor for a variable distance. In its concave free
edge is found.
3. The =round ligament= (Lig. teres hepatis), a fibrous cord which
extends from the umbilical fissure to the umbilicus; it is the vestige
of the umbilical vein, which in the fœtus carries the blood from the
placenta to the liver.
4. The =right lateral ligament= (Lig. triangulare dextrum) is a wide
fold which attaches the dorsal border of the right lobe to the costal
part of the diaphragm.
[Illustration: