NORMAL HISTOLOGY. 



bach. This is composed of a rich net-work of delicate, pale fibres, 

 at the nodal points of which microscopic ganglia exist ; after supply- 

 ing the longitudinal and outer part of the circular muscular coats, the 

 fibres obliquely pierce the latter tunic to gain the submucous tissue, 

 where they form the plexus of Meissner, which closely resembles 

 Auerbach's nervous net- work within the muscularis, possessing, how- 

 ever, smaller ganglia and somewhat closer meshes. From the plexus 

 of the submucous tunic fibres pass into the mucosa to form net-works 

 about the glands and to send fibrillae into the villi. The ultimate 

 distribution of these fibres must be regarded as still undetermined. 



THE LIVER. 



Although the liver in its development corresponds to a compound 

 tubular gland, a type which is permanently retained in many lower 



vertebrates, in the adult 



FIG. 216. condition of the mam- 



malian organ this char- 

 acter is largely masked 

 in consequence of the 

 fusion of the tubes in 

 the formation of the 

 cords of cells. 



The fibrous tissue 

 enveloping the exterior 

 of the liver is prolonged 

 into the interior of the 

 organ through the 

 transverse fissure, in 

 company with the 

 blood-vessels and the 

 bile - ducts. The de- 

 marcation of the indi- 

 vidual lobules depends upon the development of this interlobular 

 connective tissue, known as the capsule of Glisson ; when well 

 developed, as in the liver of the hog, the lobules are defined with 

 great distinctness, being completely surrounded and separated from 

 their neighbors by the connective tissue. In the human liver, on the 

 contrary, the interlobular connective tissue is very scanty, this defici- 

 ency producing poorly-defined lobules, the boundaries of which are 

 scarcely indicated by the irregular areas of connective tissue occupy- 

 ing the spaces between the approximated surfaces of three or more 

 hepatic lobules. 



The arrangement of the blood-vessels is so important in de- 

 termining the general construction of the lobule that an early con- 



Section of liver of hog, showing very diagrammatically the 

 lobules : a, interlobular connective tissue ; b, c, branches of por- 

 tal vein and of hepatic artery ; d, bile-ducts ; e, intralobular vein. 



