STRUCTURE OF THE LIVER. 



1713 



envelope, or capsule, investing the exterior, at the transverse fissure enters the 

 organ and accompanies the interlobular vessels in their ramifications as the capsule 

 of Glisson (capsula fibrosa). The distinctness with which the lobules are defined 

 depends upon the amount of this interlobular tissue. In certain animals, notably 

 in the hog, this is great, the lobules being completely surrounded and plainly dis- 

 tinguishable as sharply marked polygonal areas. In the human liver, on the con- 

 trary, the interlobular connective tissue is present in small amount, the lobules, in 

 consequence, being poorly defined and uncertain in outline. 



The Lobular Blood-Vessels. — Since the arrangement of the blood-vessels 

 is the salient feature in the architecture of the fully formed lobule, it is desirable to 

 study the vascular distribution before considering the disposition of the hepatic cells. 

 As already described, the branches of the portal vein, the functional blood-vessel 

 of the organ, ramify within the capsule of Glisson and encircle the periphery of the 

 lobule ; inasmuch as these vessels supply the divisions of glandular tissue with 

 blood for the performance of their secretory role, they correspond with the inter- 

 lobular arterioles of ordinary glands. 



Numerous minute branches are given off from the interlobular ramifications of 

 the portal vein which enter the periphery of the adjacent lobules and break up into 



Fig. 1445. 



Central vein 



•^/ ^ qO/ Portal vein 



Section of liver injected from hepatic vein, showing intralobular capillary net-work. X too. 



the intralobular capillary net-work. The disposition of the latter is in general 

 radial, the capillaries converging towards the middle of the lobule, where they join 

 to form the central or intralobular vein, the beginning of the system of the hepatic 

 veins by which the blood passing into the lobules is eventually carried into the 

 inferior vena cava. The general course of the central vein corresponds to the long 

 axis of the lobule (Fig. 1444), and hence in cross-sections of the latter the vein 

 appears as a transversely cut canal towards which the capillary vessels converge 

 (Fig. 1445). 



The capillary net-work within the lobule is composed of channels with a 

 diameter usually of about .010 mm. ; the widest capillaries — some .020 mm. in 

 diameter — are found in the immediate vicinity of the afferent and efferent veins, 

 the narrowest occupying the intermediate area. The meshes of the vascular net- 

 work vary from .01 5-. 040 mm. in their greatest dimension, those at the periph- 

 ery being broader and more rounded, while those near the centre are narrower 

 and more_ elongated. The central vein occupies the long axis of the lobule and 

 increases in size as it proceeds towards the base of the lobule, as the side of the 

 latter through which the vein escapes is termed. It begins usually about midway 



108 



