The portal vein, formed by the junction of the superior mesenteric and splenic veins, commences behind the head of the pancreas, ascends behind the first part of the duodenum, and then, accompanied by the bile-duct and hepatic artery, proceeds between the layers of the gastro-hepatic omentum to the transverse fissure, where it divides into right and left branches, of which the latter is connected with the round ligament and ductus venosus. The portal vein conveys blood from the stomach, intestines (excepting lower portion of rectum), spleen, and pancreas, and ramifies in the substance of the liver.

Portal obstruction may arise from pressure on the veins, from tumours of the head of the pancreas or adjacent parts, from cirrhosis or tumours of the liver itself, or from valvular disease of the heart (causing engorgement and ' nutmeg liver '). In such cases abdominal ascites generally occurs, the abdominal cavity becoming distended with free fluid. The circulation is so far relieved by (1) para-umbilical communication between veins of the abdominal wall and portal ; (2) communication of portal and systemic veins at uncovered surface of liver ; (3) similar communication between veins of the lower part of the oesophagus and those of the stomach ; (4) similar communication between the superior (portal) with the middle and inferior haemorrhoidal (systemic). In order to assist the circulation, an artificial anastomosis between portal and systemic venous systems has been made by bringing a portion of great omentum into contact with the subcutaneous tissues of the abdominal wall. Hemorrhoids frequently occur in portal congestion.

The hepatic artery arises from the coeliac axis, runs along the upper border of the pancreas, giving off pancreatic, pyloric, and gastro-duodenal branches, enters the gastro-hepatic omentum, and so reaches the transverse fissure. It divides into right and left branches, the cystic artery being given off from the right division, which ramifies in the portal canals. The blood is conveyed from the liver to the inferior vena cava by the hepatic veins. The portal vein, hepatic artery, and bile-ducts are surrounded by connective tissue derived from the connective tissue which invests the surface of the liver, and is known as Glisson's capsule. Thus, these structures may collapse when cut, whereas the hepatic veins are embedded in liver tissue, and hence gape when cut, and, as they have no valves, may regurgitate blood from the inferior vena cava. This point is of importance in relation to injury of the liver, which is frequently ruptured from blows or crushes. If the capsule be torn, the patient may die from haemorrhage, whereas if it remain intact, as not infrequently occurs, the patient may recover. Considerable portions of liver have been removed, however, by ligature, incision by cautery, and even by excision by knife, with success (hepatectomy), and in this connection it should be remembered that the blood-pressure in the liver is low. The liver is occasionally damaged by fractured ribs, and even extensive wounds of the liver may be recovered from. The liver very frequently becomes secondarily affected by carcinoma, many nodules forming, some of which may be easily palpated as they lie on the surface, while the organ becomes greatly enlarged. The infection of the liver is generally comparatively early in carcinoma of the stomach, from which the infection is believed to be conveyed by the portal vein (as is likewise conveyed infection from carcinoma recti).

The lymphatics of the liver are arranged in two sets- superficial and deep. The former lie under the peritoneal covering, and drain to the hepatic glands in the lesser omentum, lumbar, anterior mediastinal glands, and right lymphatic duct. The latter accompany the hepatic and portal veins, and drain to the hepatic glands and to the thoracic duct. The nerves are derived from the left pneumogastric and solar plexus.

The liver is not infrequently the seat of abscesses. These may occur in connection with pyemia, when they are small, multiple, and superficial ; or from ulcerative conditions of the bowel (the infection probably being conveyed by the portal vein) or biliary passages, when the abscess is generally large, single, and deeply seated. The pyaemic multiple abscesses occur frequently in connection with pyogenic head affections- as, for example, suppurative sigmoid sinus thrombosis-but are rare in pyaemia from urinary affections or burns. 'Tropical abscess,' which occurs in connection with dysentery, is a good example of the solitary type. While at first deeply seated, the abscess may progress either upwards towards the diaphragm or down toward the peritoneum. In the first case, it gives rise to cough from irritation of the vagus filaments in the liver, and to pain in the right shoulder region from irritation of the right phrenic (both in the liver and the diaphragm), which communicates with the superficial descending cutaneous branches of the cervical plexus. The abscess may burst into the pleura, but, more generally, from soldering of its layers, bursts into the lung, and may be coughed up through the bronchi, or may cause suffocation. Where the abscess proceeds downwards, it may burst into the stomach, intestine, or peritoneal cavity. The abscess may be attacked through the abdomen (generally in two stages, to permit of soldering of the peritoneum round the wound, thus shutting off the peritoneum), or by the transpleural route.

The liver is the most common seat of hydatid cysts, the embryo boring its way from the intestine into the portal vein, and being thus conveyed to the liver. Such cysts may attain a large size, and sometimes burst into the lungs. They may be attacked by either of the routes mentioned for abscess. The large bile-ducts which converge to the transverse fissure, to form by their junction the right and left hepatic ducts, present numerous dilatations, which may act as reservoirs when the gall-bladder has been removed or rendered insufficient. The two hepatic ducts join to form the hepatic duct, which runs downwards for 1 inch in the portal fissure to the point where, joined by the cystic duct, it forms the common bile-duct.

The gall-bladder is a thin-walled, pyriform sac, about 3 inches long, lying obliquely on the under-surface of the liver, to which it is attached by connective tissue. Below, it is in contact with the transverse colon in front, and duodenum behind. It is invested with peritoneum, except, as a rule, on its upper surface. Its fundus is directed downwards, forwards, and to the right, and when the bladder is full presents in the angle between the outer border of the rectus and the costal margin, opposite the ninth cartilage. The neck presents an S-shaped curve (and presents internally a somewhat spiral folding of the mucous membrane, which is said to obstruct the passage of gall-stones), and ends in the cystic duct, which is slightly narrower and longer than the hepatic duct which it runs backwards and inwards to meet. The two ducts join at the mouth of the portal fissure to form the common bile-duct, which, about 2 inches long, runs down in front of the foramen of Winslow, between the layers of the lesser omentum, with the portal vein behind and the hepatic artery to the left. It now descends behind the first part of the duodenum, and then between the pancreas and second portion of the duodenum, where it meets the pancreatic duct, along with which it runs obliquely through the duodenal wall, to open on a common papilla 4 inches beyond the pylorus. The gall-bladder is not infrequently distended, sometimes from the impaction of a stone in the cystic duct, or an accumulation of stones in the bladder itself, or from obstruction in the common bile-duct, by malignant growths of the duodenum, pancreas, etc. Where greatly distended, it has been mistaken for an ovarian cyst, the mass extending below the umbilicus. While at first the bladder is distended with bile, in long-standing cases, where the duct becomes occluded, it may only contain clear fluid. It also sometimes contains pus. The irritative process extends through the walls of the bladder to the surrounding structures, and thus the bladder may contract adhesion to the duodenum, colon, etc. In some cases where a large stone has been lodged in the gall-bladder, and such adhesions have formed, the stone has ultimately ulcerated its way through into the duodenum, and become impacted in the ileum, causing intestinal obstruction. In other cases it has ulcerated its way through the anterior abdominal parietes. In operating on the gall-bladder, an incision is made either vertically through the rectus or right semilunar line, or obliquely beneath the costal margin, and the bladder and ducts exposed and examined.

For the removal of stones in the bladder after aspiration of fluid contents, cholecystotomy may be performed, the bladder being subsequently closed by stitching ; or a cholecystostomy, in which the opened bladder is stitched to the abdominal wound, and allowed to heal by granulations. Choledochotomy is the operation for removal of a calculus in the common bile-duct by longitudinal incision, which is subsequently stitched (the part being surrounded by gauze packing, as leakage is common). One or two lymphatic glands lie in the gastro-hepatic omentum close to the neck of the gall-bladder, which, when enlarged or calcified, may be mistaken for gall-stones. Where the stone is lodged in the lower extremity of the common bile-duct (ampulla of Vater), it maybe expressed into the duodenum or crushed. If a cutting operation be necessary, difficulty is experienced, the pancreas or duodenum frequently requiring to be cut into. Cholecystectomy, or removal of the gall-bladder by stripping the peritoneum and ligaturing the neck and cystic artery, may be performed for new growths, occlusion of the duct, etc. Cholecystenter ostomy consists in joining the gall-bladder and duodenum so as to make a fistula in cases where the common bile-duct is obstructed. The nerve-supply of the gall-bladder is from the eighth and ninth segments of the cord through the great splanchnic and cceliac plexus ; and hence in passage of gall-stones pain may be referred to the parietes over the epigastrium, right hypo-chondrium, and lumbar region (biliary colic).