Page images
PDF
EPUB

ducts passing to the lobules are few in number, and have a short and simple course. In the frog and newt, and in the class of fishes generally, the markings are very indistinct, and there is no regular arrangement of small ducts round portions of hepatic tissue similar to that which exists in mammalia. In the uninjected state, and without previous preparation, these small ducts are so stretched and torn by manipulation that it is quite impossible to distinguish the striated appearance which is produced from ordinary fibrous tissue. The lines between the different lobules of the human and other livers, seen by the unaided eye, are, in the majority of cases, due to a difference between the cells at the surface of the lobule close to the ducts, and those in the interior. In the former situation the cells often contain many oil globules, which are white by reflected light, and appear like a distinct line of separation, while in the latter they frequently contain colouring matter alone.

The small ducts which have been referred to in the last paragraph have been represented in figs. 3, 4, and 5. Although numerous branches have been successfully injected in the preparations from which these drawings have been taken, I feel convinced that, from an examination of such specimens alone, a very imperfect idea can be formed of the vast number of these finest ducts existing in the interlobular fissures of a healthy liver.

In the human foetus, the separations into lobules are very distinctly marked, but the appearance is not due to the presence of a fibrous capsule, or to the existence of a large quantity of fibrous tissue; for in a well prepared specimen every portion of space between one of the lobules, or spaces mapped out, and its neighbour's, can be seen to be occupied with branches of the vein, artery, and duct, which may be injected. In such a preparation the complete absence of any structure like fibrous tissue, is remarkable.

very

The mapping-out is really produced by the different appearance of the little elementary portions of liver which are made up of the secreting elements of the gland, which are more or less coloured, and the intervals between these, in which there are no liver-cells, and which are colourless or nearly so. In these intervals the portal vessels and duct reach the circumference of the lobule,

and become continuous with the capillaries and cell-containing network of which the secreting structure is composed.

The interlobular spaces are enormously increased in extent in certain cases of disease where the liver-cells at the margin of the lobule have degenerated. This increase, of course, takes place at the expense of the secreting structure of the lobules, which in a section are seen to be much diminished in size. I have a specimen of diseased liver in which the interlobular spaces are as wide as the lobules. That this increased extent, is due to an alteration in the secreting structure of the lobule is certain, because the network which originally contained cells can be distinctly traced, and in many situations contains biliary particles. Such a specimen would have been formerly described as produced by a thickening of Glisson's capsule. The interlobular spaces then are occupied only by branches of the vessels and duct which lie in close proximity to each other, and no structure corresponding to the description of Glisson's capsule is to be detected in this situation.

With reference to the physiological arrangement of the elementary tissues of which the gland is composed, it may, I think, be said that the livers of all vertebrate animals are arranged so as to form more or less isolated portions, or lobules; but in a strictly anatomical sense, the term must be confined to the liver of the pig, since it is only in this animal that the individual lobules can be separated from one another.

25

CHAPTER III.

OF THE VESSELS OF THE LIVER.-PORTAL VEIN.-MANNER IN WHICH THE APPEARANCE OF A VENOUS RING IS PRODUCED. -ARRANGEMENT OF VENOUS BRANCHES IN THE COATS OF THE GALL-BLADDER, TRANSVERSE FISSURE AND LARGER PORTAL CANALS.-HEPATIC ARTERY.-BRANCHES, TO THE CAPSULE, IN THE PORTAL CANALS, OPENING INTO THE

PORTAL CAPILLARIES.
BRANCHES.
DUCTS.

[blocks in formation]

HEPATIC DUCT.

[blocks in formation]

- EPITHELIUM. PARIETAL SACCULI. OFFICE OF VASA ABERRANTIA AND SACCULI.-GALL-BLADDER.-NERVES AND LYMPHATICS.-HEPATIC VEIN.-HEPATIC VEIN IN SEAL.

PORTAL VEIN.

THE large portal vein is formed by the union of the veins of the stomach and intestines, the pancreatic and splenic veins, and the veins of the mesentery, omentum, and gall-bladder. The larger trunks of the portal vein pursue their course in the portal canals, as has been described in page 18. The smaller branches may be said, in general terms, to be arranged round the lobules. These often give off twigs to the neighbouring lobules in a stellate manner. The branches upon different sides do not anastomose so as to encircle each lobule with a venous ring, as many authors, following Kiernan's figures, have described and represented, but communicate with each other only through the intervention of capillaries, as Bowman, Kölliker, and some other observers have stated. Gerlach, on the other hand, gives drawings of these anastomosing trunks, the diameter of which he represents as the same round the entire circumference of the lobule. I have not been able to demonstrate such an appearance by any mode of preparation. Even in the pig there is no vascular ring, although to the unaided eye it might appear so. Interlobular branches of the portal vein in the pig's liver are represented in fig. 10. The drawing gives a good idea of their general arrangement. The capillaries are only partially injected. In the liver of the human subject, and in livers allied to it, small branches of the portal vein can

often be traced from the interlobular fissures into the lobule, breaking up into capillaries as they go.

Manner in which the appearance of a Venous Ring is produced. -In dried preparations, owing to the close approximation of trunks which in the recent state had occupied very different planes, an appearance as if the smaller trunks communicated with each other, and thus encircled the lobule in a venous ring, is undoubtedly produced. That such an appearance is fallacious is proved by carefully examining well injected specimens in fluid. For this purpose it is better to use a transparent injection, which can be examined by transmitted light. Very rarely, however, small branches of the vein do anastomose, but this communication is quite exceptional, and a similar anastomosis even occurs, sometimes between branches of the hepatic vein, as represented in fig. 6. The diagramatic representations of most authors would lead to the conclusion that such an arrangement, in the case of the portal vein, was constant, which is not the case.

The mode of distribution of the small branches of the portal vein, in the human subject, is represented in figs. 3 and 4; in the pig, figs. 10 and 12, and in the eel, fig. 54.

Arrangement of Venous Branches in the coats of the Gallbladder, Transverse Fissure, and larger Portal Canals.-In the coats of the gall-bladder, in the transverse fissure, and in the large portal canals of the human liver, there exists an intimate network of veins, which pour their blood into the large branches of the portal vein. The arrangement of these branches is peculiar and exceedingly beautiful, especially in the gall-bladder, in the coats of which there exists an abundant venous and arterial network. Each branch of artery is accompanied by two branches of vein ; and when these sets of vessels are injected with different colours, a very beautiful appearance is produced. I have a preparation in which the artery has been injected with vermilion, and the vein with white lead.

HEPATIC ARTERY.

Branches to the Capsule.-Many branches of the artery pass to the capsule of the liver, in which they ramify abundantly, forming a network having large meshes. These capsular branches and

their anastomoses, are readily injected in the liver of the fœtus or child. They are beautifully seen upon the surface of the pig's liver, and encircle each individual lobule with a ring.

Branches in the Portal Canals.-Each branch of portal vein, in the portal canals, is accompanied with at least one branch of the hepatic artery, figs. 4, 5, 12, 28, 29, and frequently by two or three which communicate with each other by anastomising branches.

The artery gives off numerous branches in the portal canals. The greater number of these are distributed upon the coats of the ducts. The thick walls of the larger ducts are abundantly supplied with arterial blood, fig. 9; but the smaller branches of the duct, the coats of which are extremely delicate, pass through the meshes of an arterial network, fig. 8. In the pig this network may be very readily demonstrated upon the surface of each lobule, as represented in figs. 7 and 8, where it is only imperfectly injected; but in the human subject, and in mammalia generally, the branches are less numerous, and are seen only in the interlobular spaces; other branches supply the coats of the portal and hepatic veins. The greater quantity of blood, after passing through these small arteries, is collected by venous radicles, which empty themselves into branches of the portal vein.

Branches which open into the Portal Capillaries of the Lobule.A certain proportion, however, of the blood is undoubtedly poured into the capillaries of the lobule, as may be readily proved by injection with different colours. Some very small straight arterial branches may be traced from the portal aspect of the lobule, or from the interlobular fissures, for a short distance into the interior, where they join the capillaries, near the portal surface of the lobule.

The whole of the arterial blood, therefore, which supplies nutriment to the several structures of the liver, passes through the capillaries of the lobule before it is returned to the heart, and no doubt furnishes a small portion of the material from which the bile is formed. The termination of some of the lobular branches of the artery is represented in the frontispiece at g, in fig. 2 at d, and in fig. 7 at b. The hepatic artery was originally regarded by Kiernan as one of the sources of the blood conveyed to the

« PreviousContinue »