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come off from the trunks are connected by smaller branches, which arise not far from the point at which they are given off, as represented in fig. 19. I have been able to prove, from very many injections, that these communications are very numerous indeed. Similar anastomoses occur to some extent in the case of branches of moderate size in the portal canals of the human liver; and in very good injections small branches coming off from a trunk at short intervals may be seen to communicate freely with the trunk itself, and with each other, by numerous intermediate branches, so that a network is formed at a short distance from the parent trunk (figs. 39 and 40 c). The meshes of this network are most variable in size and shape, and the tubes are more dilated in some places than in others (fig. 40a). Some of these branches are composed simply of basement membrane and epithelium, but the largest have a fibrous coat, though much thinner than that of the duct itself. Branches of the vein and artery, and of lymphatics (in the case of the larger portal canals), ramify among these ducts, and lie in the meshes of the network. In very good injections this network of branches of the duct is demonstrated in the adult, but in the fœtus the communications are to be shown with less difficulty, although the branches are not so tortuous and are less complex.

In the dog, and also in the calf, I have observed similar communications, but not so numerous as in the human subject.


The smallest branches of the duct may be readily followed, in tolerably good injections, to the surface of the line of hepatic cells, which bounds the portal canals, and not unfrequently they may traced among these cells, in the human, and other livers. In the pig, the trunks may be seen gradually breaking up into their smaller branches, which are applied to the capsule of the lobule, and which appear to anastomose only very rarely, as above remarked. In the human liver an irregular network, in good injections, is to be demonstrated close to the larger branches of the ducts, and might be termed an interlobular network; but the arrangement is certainly not universal, nor does it seem to me to be sufficiently extensive to render it necessary to give it any special name: indeed, I have not been able to demonstrate it in the pig, seal, rabbit, horse, cat, or monkey. I am not prepared to affirm its absence in the above

mentioned animals, but only remark that I have not been able to demonstrate it, and do not think that it exists.

It may be stated generally, that small branches of ducts carry off the secretion from that part of the lobule to which they are distributed. These small branches unite to form slightly larger ones, and these, again, to form others. The smallest branches sometimes pour their contents at once into interlobular branches ;—in other cases they are connected by a few transverse branches,—and sometimes, they form an irregular network before they are connected with the interlobular ducts. This network, when present, is of a very different structure, and cannot be compared with that within the lobule described in Chapter IV. The ductal network exists in the most perfect form in the liver of the pig when this is not very fatty (fig. 51). When, on the other hand, the liver is fatty, this network is distended with ordinary hepatic cells containing much fat and free oil globules in considerable number.

Of the finest Branches of the Ducts, and of their junction with the tubes of the cell-containing network, in Mammalia.—It has been already stated that in injected preparations the smallest branches of the ducts can be traced up to the liver-cells. The walls of the

small ducts are composed entirely of basement membrane, which is lined with epithelium, described in page 61. These ducts do not always lie in such close contact with the smallest branches of the vein, as is invariably the case with the larger trunks.

In many animals, particularly in the rabbit, and, to a less extent, in the human subject, and in some birds (turkey, fowl), the smallest branches of the duct are connected together so as to form a lax network of ducts which is continuous with the lobular cell-containing network, as represented in fig. 30. The branches are readily distinguished by their small diameter, and by the little granular cells of epithelium within them.

Some of the finest branches of the duct often appear to lie amongst the most superficial portion of the cell-containing network without being immediately connected with the tubes or cells in this part, but they may be followed for some distance, and may be seen to join a portion of the network which lies at a deeper part of the lobule;

the tubes at the superficial portion of the cell-containing network being continuous with small ducts which do not pass into the lobule. This point is well shown in fig. 33, taken from a drawing of the seal's liver, where two ducts in the upper part of the figure are seen to join the superficial part of the network, and another in the lower portion, is observed passing for a short distance amongst the tubes of the cell-containing network.

One of these penetrating branches has been figured by Gerlach, and, as he very justly observes, these branches are much narrower than the cells between which they lie, and hence concludes, very properly, that they cannot contain liver-cells. He supposes that they terminate by open mouths, into which the bile passes from narrow inter-spaces between the cells; but that this is not the case will presently be shown.

In the pig, numerous fine branches having reached the surface of the capsule, perforate it, and are immediately connected with a dense network, forming the most superficial portion of the cellcontaining network, and consisting of very fine ducts, the tubes of which often contain small cells, granular matter, and perhaps oil globules, but usually no cells of the ordinary size are to be found within them; and, in consequence, the diameter of the tubes is much less than at a greater distance within the lobule (fig. 51). When the liver is very fatty, however, this part of the cell-containing network does contain cells filled with oil globules, as is shown in fig. 27, in which the very narrow ductal portion of the tube is seen to dilate considerably at the point where it contains liver-cells. The epithelial cells in the duct can often be traced quite up to the point which distinguishes the efferent duct from the secreting portion of the tube. This is well shown in fig. 27, which was taken with the camera from a preparation still in my possession; and which demonstrates these interesting points almost as clearly as when it was first mounted, upwards of two years since. The narrow ducts, and the wide secreting tubes, both contain a very little injection; and, in consequence of their accidental isolation from adjacent parts of the network, their continuity is seen distinctly. The delicacy and extreme narrowness of the ducts will readily explain the difficulty of demonstrating their continuity with the cell-containing network; for they almost invariably

break at the constricted portion, when an attempt is made to isolate them; and, unless this isolation can be effected, it would be impossible to prove that such an arrangement really exists. In this preparation, by an unusually lucky accident, the cell-containing network has broken, instead of the narrow portion of the duct, which is protected, as it were, by lying upon the walls of a small artery. The further continuity of the network is shown by dotted lines. I have seen the same point in several specimens, but never in one which shows a greater number of minute ducts, and their points of connexion with the tubular network in which the secreting cells lie, with greater distinctness. These narrow ducts are only 1-3000th of an inch in diameter; while the expanded portion, in which the liver-cells lie, and with which they are immediately continuous, is upwards of 1-1000th of an inch in width.

The connexion between the finest ducts and the cell-containing network, from an injected specimen of the human liver, is represented in fig. 46; the hepatic cells have been much altered in preparing the specimen from which the drawing was copied.

In fig. 42 is shown a similar arrangement in a portion of human liver, which had been treated with soda, and kept for some time in strong syrup. Here the epithelium of the ducts is well shown, but the specimen has been flattened somewhat by the pressure of the thin glass. Fig. 41 is a representation of another section of the same liver, which has not been subjected to pressure, in which the narrow ductal part of the tube contrasts remarkably with the wide secreting portion which is continuous with it. In the human foetus, the connexion between the duct and cellcontaining network is shown in fig. 39, at a, and in fig. 40 it is represented in the liver of the calf. In the seal, the hepatic cells are small, and injection readily passes into the tubes which contain them. The small ducts are comparatively few in number, but their course in this animal is very easily traced, and they can be well seen through the thin wall of a small portal vein which has been injected with clear size. In fig. 28, at c, this point is well shown upon the surface of a branch of the portal vein, and in fig. 33 the connexion between the ducts, and the cell-containing network in the liver of the same animal is represented.

Fig. 30 is a copy of a drawing of a thin section of rabbit's

liver, taken from a thin and emaciated animal, in which the cells were much smaller than natural, and the diameter of the tubes much less than in a healthy state. In many situations the tubes contained only granular matter, and no cells could be distinguished. Narrow granular lines communicating at intervals with each other, were seen separated by wide clear spaces (capillaries). The injection ran very readily, and in some places distended these tubes to the extent shown in fig. 32, and thus the clear capillary space was obliterated. In this specimen the very fine ducts were injected to a greater extent than can usually be effected; but even here I am persuaded that the injection has not entered into many of them. I believe it to be nearly impossible to inject all or even the greater number of the minute ducts; for by the pressure which 'those filled with injection must necessarily exert upon the adjacent ones, the latter become completely occluded, and no injection whatever can enter. Their extreme tenuity, and the number which lie in close apposition, preclude the possibility of demonstrating them in the uninjected state, except in a few rare instances by a peculiar method of preparation.

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Birds. In the turkey, and also in the fowl, I have been able to trace the continuity of the ducts and cell-containing network in injected specimens. The abundance of epithelium in the ducts forms a great obstacle to perfect injection, and the excessive delicacy of the capillaries prevents the injection of much water without rupture. From this cause I failed in many attempts to obtain demonstrative preparations of the arrangement in the bird's liver.

In the chick of the 15th day, and also in that of the 21st day, the continuity was clearly made out in some preparations which had been previously hardened in alcohol and soda.

Reptiles. In the newt I have traced the course of the ducts in an uninjected specimen, and have succeeded in making a good injection of the ducts of the adder, in which animal the continuity of the very narrow ducts, with the wide tubes containing the liver-cells, could be clearly traced.

Fishes. In the investigation of the anatomy of the ducts in the class of fishes, the greatest difficulties presented themselves, and very numerous were the failures which I met with in trying to inject them. The difficulty arose partly from the delicate

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