226 Royal Society. 



the import of which, in the situation they occupy, is doubtless the 

 same as that of the similar masses existing in fishes. 



In Birds, the parenchyma of the liver is remarkably free from oily 

 or retained biliary matters; it often consists almost wholly of free 

 nuclei and granular matter, with scarcely a single perfect cell ; the 

 excretory ducts often greatly resemble those of reptiles, sometimes 

 rather those of mammalia; the essential character is, however, always 

 the same, namely, that they terminate without forming any important 

 connexion with the jiarenchyma. 



In Mammalia, the parenchyma of the liver consists usually of per- 

 fect cells, which are arranged often in linear series of considerable 

 length, radiating from the axis of each lobule ; these unite at variouf 

 points with each other, so as to present a more or less decidedly 

 plexiform appearance. Each lobule, as described by Mr. Kiernan, 

 is separated from the adjacent ones by the terminal twigs of the 

 portal vein, and to a greater or less extent by a " fissure," though in 

 most animals the lobules are continuous with each other both above 

 and below the fissure. The elaboi'ation of the secreted product 

 seems to be most completely effected in the cells adjoining the 

 margins of the lobules, which are often seen to contain a larger 

 quantity of biliary matter than those in the interior, and to be appa- 

 rently in the act of discharging it into the fissure; the margin of 

 the lobule then presents an irregular surface with large globules of 

 the secretion clustering together all over it. The capsule of Glisson 

 surrounding the vessels in the portal canals gives a fibrous invest- 

 ment to those surfaces of the lobules which are towards the canal ; 

 but when it has arrived in the fissures, it forms a continuous mem- 

 brane lining the surfaces of opposite lobules ; this membrane is often 

 truly homogeneous, and closely resembles the basement tissue : there 

 appears occasionally to be a delicate epithelium on its free surface ; 

 but this, as well as the membrane itself, is often absent, when the 

 margin of the lobules is in that condition which has just been de- 

 scribed and which may be termed active. The minute branches of 

 the hepatic duct as they approach their termination undergo a re- 

 markable alteration in their structure ; they lose their fibrous coat, 

 which blends itself with the membranous expansions of the capsule 

 of Glisson ; their basement inembrane becomes gi-adually indistinct, 

 and at last ceases to exist, and the epithelial particles no longer 

 retain their individuality, but appear to be reduced to mere nuclei, 

 set very close together in a faintly granular basis substance. The 

 mode of their termination is not uniformly the same; frequently they 

 present distinctly closed rounded extremities, between one and two 

 thousandths of an inch in diameter; at other times they seem to 

 cease gradually in the midst of fibrous tissue, the nuclei alone being 

 disposed for some little way in such a manner as to convey the idea 

 of a continuation of the duct. These ducts can seldom be dis- 

 cerned in the fissures, but have several times been seen in the 

 " spaces," where several fissures unite ; they do not form anything 

 like a plexus between the lobules. From the anatomical relation of 

 the ducts to the parenchyma, and from the circumstance that a 



