546 SPECIAL HISTOLOGY. 



•which accompany the portal vein, and, in animals, at least, the hepatic 

 veins also. Both kinds of vessels are connected and proceed partly 

 through the dicqjh-agm into the thorax, partly to small lymphatic 

 glands in the 'porta hepatis, and to the intestinal plexus. The lympha- 

 tics of the gall-bladder are also exceedingly numerous. 



The nerves of the liver are relatively very abundant. They arise 

 from the sympathetic, and, in a smaller proportion, from the vagus, and 

 are chiefly distributed with the hepatic artery, around which they form 

 closer and wider networks without ganglia. They always contain, 

 together with many fine tubules, and " Bemak's fibres," a few thick 

 fibres, and may be traced ; 1, to the gall-bladder and large biliary 

 ducts ; 2, in Glisso7is capsule as far as the interlobular arteries, where 

 their finest twigs, of 0-008-0-012 of a line, contain only nucleated 

 fibres ; 3, to the hepatic veins ; and lastly, 4, into the coats and liga- 

 ments of the organ. 



§ 163. According to the latest observations, particularly of Bischoff 

 and Bemak, the development of the liver may thus be best understood. 

 The primary rudiment of the liver, which appears at a very early period 

 (about the 55-58 hour, in the Chick ; in Mammals, after the Wolffian 

 bodies and the allantois) consists of tAvo masses of cells, an external, 

 proceeding from the fibrous membrane of the intestine, and an internal, 

 epithelial, which at first form a simple, and afterwards a dichotomously 

 divided sac. S'olid processes, the hepatic cylinders of Reraak, are now 

 developed from the epithelial lamina, which, as in the intestine, consists 

 at first of round cells, probably in many layers, by the multiplication of 

 its cells, and extend into the outer lamina, branching out and anastoynos- 

 ing, whilst, at the same time, the cells of the outer lamina included in 

 the meshes of this network, multiply and become successively changed 

 into vessels, nerves, connective tissue, &c. The difficulty is to say how 

 this peculiar, reticulated parenchyma of cells and rudimentary vessels 

 becomes ultimately arranged as we know it to be. In the first place, as 

 regards the hepatic-cell-network and the islets or lobules of the complete 

 liver. They evidently proceed from the further growth of the original 

 hepatic-cell-network, to which by a continual new development of cells, 

 fresh processes are added, which unite into new networks, so that the 

 hepatic-cell-network of the adult liver is the direct progeny of the ori- 

 ginal reticulation. More detailed information concerning the separate 

 steps of the formation of the hepatic-cell-network, is at present wanting ; 

 yet from what is known it would appear to take place in somewhat dif- 

 ferent modes. Sometimes, in the subsequent stages, free cylindrical 

 processes of the hepatic-cell-network do not exist to any extent, but it 

 would appear to increase by the continual addition of new meshes at its 

 edges, perhaps also by the constant elongation of the existing columns 

 of hepatic cells and the development of fresh anastomoses between them ; 



