504 



MANUAL OF HISTOLOGY. 



be necessary, in the first place, to consider the arrangement of its llood- 



The vascular system of the liver possesses this peculiarity, that it receives 

 its blood from two sources, namely, from the hepatic artery and portal 

 vein. The last of these conveys a much larger proportion of blood to the 

 organ than the former, which takes part less in the elaboration of bile 

 than in the nutrition of the hepatic tissue. Its branches, accompanying 

 the divisions of the portal vessels and bile ducts, are distributed, in the 

 first place, as vasa nutrientia to the coats of both (rami vasculares) ; and, 

 secondly, to the serous covering of the liver, as far as which they pene- 

 trate (rami capsulares), forming there a wide-meshed capillary network. 

 The veins derived from these empty themselves into the ramifications of 

 the portal vessels, so that the latter may be injected from the hepatic 

 artery, and vice versa, if the canula be inserted into the portal vein the 

 injection may be driven into the hepatic artery. Finally, a few very 

 small twigs (rami lolmlares) sink into the peripheral portion of the capil- 

 lary network of the hepatic lobules. Through these the hepatic artery 

 takes some part, at least in the production of the bile. 



The portal vein, with whose course we take it for granted the reader is 

 already acquainted from the study of general anatomy, forms, with its 

 terminal branches, the vence interlobulares of Kiernan, or vence periphericce 

 of Gerlach. These are fine tubes of 0'0338 0*0451 mm. in diameter, 

 which surround the lobules either in the form of short (in man) or long 

 (rabbit) loops, or, as is pre-eminently the case in the pig, in the form of 

 regular rings, breaking up rapidly on all sides, either into finer branches 

 or immediately into capillaries. In fig. 501 we have a representation 

 of what takes place here : a twig of the portal vein is seen passing 

 through the middle, and giving off on either side the rami-interlobu- 



lares, which terminate eventually 

 in a capillary network after en- 

 circling the lobules. 



This network, the most highly 

 developed which exists in the body, 

 consists of vessels from 0-0090 to 

 0'0126 mm. in diameter, whose 

 delicate walls can only with diffi- 

 culty be demonstrated. The meshes 

 formed by these are very dense, mea- 

 suring only from 0'0226 to 0'0451 

 mm. They are either rounded, 

 square, or triangular in figure, and 

 lie, for the most part, with their 

 long axis, often rather indistinctly 

 directed, towards the centre of the 

 lobules. 



In the interior of the latter the 

 capillaries either form, by their 

 rapid confluence, a single hepatic 

 venous radicle, or, what is more 

 frequently the case, two or more 

 such. These may, in some instances, be met with in much larger num- 

 bers. The hepatic twigs are situated in the centre of the lobules ; they 

 are from 0'5640 to 0'0677 mm. in diameter (Gerlach), and have been 



Fig. 501. RabbiWi liver injected, showing a portal 

 branch, the vence interlobulares, the capillary net- 

 work, and a vena intralobularis in the centre of 

 a lobule. 



