THE ABDOMEN 8^7 



lobe, pass to the hepatic glands. (2) The lymphatics from the 

 posterior part of the inferior surface of the right lobe pierce the 

 diaphragm, and end in the caval glands. (3) The lymphatics from 

 the greater part of Spigel's lobe pierce the diaphragm, and end in 

 the caval glands ; whilst those from the lower part of this lobe pass 

 to the hepatic glands. (4) The lymphatics from the inferior surface 

 of the left lobe pass to the hepatic glands. 



Deep Lymphatics. — ^These vessels form two distinct sets. Some 

 of them accompany the branches of the portal vein, and, having 

 emerged through the portal fissure, they terminate in the hepatic 

 glands. Others pass with the hepatic veins to the caval fossa of 

 the liver, and thereafter they enter the thorax along with the 

 inferior vena cava, their destination being the caval glands. 



Nerves. — The nerves of the liver are derived from the hepatic 

 plexus, which is an offshoot of the coeliac plexus, that in turn being 

 derived from the solar plexus of the sympathetic system. The 

 coehac plexus, though principally composed of sympathetic fibres, 

 is reinforced by a few twigs from the right pneumogastric nerve. 

 The hepatic plexus accompanies the hepatic artery to the portal 

 fissure, where it receives branches from the left pneumogastric 

 nerve, which have ascended from the antero-superior surface of 

 the stomach between the two laj-ers of the gastro-hepatic omentum. 

 In the liver the nerves, which are chiefly non-medullated, are dis- 

 tributed to the walls of the bloodvessels and ducts, penetrating as 

 far as the interspaces between the hepatic cells. 



DevelopmeDt of the Liver. 



Liver. — The hepatic cells and the epithelium of the bile-ducts are of ento- 

 dermic origin, whilst the connective tissue of the gland and its vascular con- 

 stituents are developed from the mesoderm. 



The rudiment of the liver appears as a longitudinal groove on the inner 

 aspect of the ventral wall of the duodenal portion of the primitive gut. This 

 groove gives origin to a diverticulum or evagination of the entoderm of the 

 ventral duodenal wall, called the hepatic diverticulum or liver-bud, which has 

 at first a wide communication with the gut. At a later period this com- 

 munication becomes constricted, and forms a pedicle, which, after undergoing 

 elongation, gives rise to the common bile-duct. From this pedicle, close to 

 the duodenal wall, the ventral diverticulum of the pancreas arises. 



The hepatic diverticulum or liver-bud invades the lower or caudal layer of 

 the septum transversum, composed of mesoderm, within which it bifurcates, 

 the two divisions representing the right and left hepatic ducts. 



The cells of these two divisions of the hepatic diverticulum undergo pro- 

 liferation within the mesoderm of the lower layer of the septum transversum, 

 and thereafter each division breaks up into a number of solid trabeculae, 

 which are known as the hepatic cylinders. These cylinders give off secondary 

 solid trabeculae, and these again ramify extensively. The subdivisions of the 

 various trabeculae anastomose freely, and in this manner intricate networks 

 are formed around the vitelline and umbilical veins, which veins traverse the 

 septum transversum as they pass to the sinus venosus. The hepatic cylinders 

 invade these veins, carrying the endothelial walls of the vessels before them. 

 The veins are thus freely .subdivided into blood-channels, which are known 

 as sinusoids. These sinusoids form capillary networks, which occupy the 

 meshes of the net\vorks formed by the hepatic cylinders. 



Many of the solid trabeculae become tubular, and give rise to the bile- 

 capillaries or bile-canaliculi, and bile-ducts. Others give rise to the hepatic 



