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distribution through the portal canal, fig. 373, g, where the minute branches form vaginal plexuses,' sending off interlobular branches which terminate in the lobule by a capillary plexus communicating and localised with the portal one. The meshes of the radially arranged plexuses, fig. 375, are occupied by organites which subsist by endosmotic intussusception and assimilation of blood-elements, modify them by interchange of other elementary combinations, then perish by rupture or solution of their walls. These bodies, called hepatic cells,' much exceed in size the monads of infusoria,' being about both inch in diameter; but, like them, they have a hyaline granulated nucleus, which contrasts by its refractive brightness with the tawny yellow of the minuter granules of the main contents of the cell, in which also float oil-globules. These contents, exuded or set free, fill the intervals of the nucleated cells,' and form the 'bile,' or brief equivalent of bile vesicles without proper walls.' When an epithelium is discernible, separating them from the capillaries,3 the bile-ducts may be said to commence. The inductive figure given by Kiernan of the intralobular or initial bile-conduits, fig. 375, receives support from the recent careful researches of Hering in the liver of the rabbit:

375

2

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he describes them as forming a plexus with polygonal meshes from which the canals are continued to form the interlobular ducts, a, a; from these are continued the ' vaginal branches,' fig. 373, h, which progressively unite to form the hepatic ducts. These, in Man, emerge, two in number, at the portal fissure: in more divided livers the liberated ducts are more numerous; but all unite, as a rule in Mammals, into one trunk, which, in those having a gall-bladder, joins the cystic duct to form the ductus communis choledochus.' This duct, fig. 376, a, penetrates the duodenum distinctly from the pancreatic duct, b, both run obliquely between the several

1 Such, e.g. as the Monas atomus, 20th line in diameter.

2000

2 Ein Gallencapillarystem ohne eigene Wandung.' CLIX". p. 241.

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3 The 'when' or where' such epithelial walls are gained, forming a beginning of proper conduits for carrying off the bile from the interspaces of the formative cells, may long be debateable ground with Micrographers; as now between Beale, Budge, and Hering. CLIX". p. 241.

46

Ein Netz mit polygonalen Maschen,' CLIX", p. 241. Kiernan obtained a view of anastomosing biliary ducts in part of a lateral ligament of the human liver; CLVII". p. 769, pl. xxiv. fig. 4.

tunics, c, d, e, of the gut, in Man, to the extent shown in fig. 376, before uniting to form the common receptacle within the terminal prominence.

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376

The carrying arrangements' of the bile are, thus, on a more concentrated plan in the present than in lower classes of Vertebrates. The human cystic duct shows a series of crescentic folds of the lining membrane, directed obliquely round the canal, and so arranged as to give the appearance of a spiral valve. Numerous minute follicles, either branched or clustered, open upon the mucous tract of the bile-ducts: in the smaller branches their orifices are in two opposite longitudinal

rows.

From the arrangement and localisation in the lobule of the capillaries of the two systems of veins, determined, together with most that is of importance in hepatic structure, by the admirable research, skill, and patience of KIERNAN, an explanation has been afforded of appearances otherwise unintelligible or misleading. When the capillaries of the hepatic vein are gorged, as is usual in an early stage of congestion, the flattened surfaces of the lobules on the superficies of the liver present the appearance in fig. 377. When the portal capillaries

377

e dc Hepato-pancreatic ampula human: magn.

Lobules of liver with congested hepatic veins.
CLVII".

are congested, the peripheral
deeper colour, as in fig. 378.

1

Lobules of liver with congested porta veins.
CLVII".

parts of the lobules present the
So, in examining portions of the
cortical' and 'medullary' substances of some

authors; of red' and 'yellow' substances of others. See CLVII". p. 763.

liver of lower Mammals, as in that of the squirrel figured by J. Müller,' fig. 379, the uncongested pale peripheral portions of

abdominal viscera, and by the degree in which it may be affected by inflections of the trunk.

§ 339. Pancreas of Mammalia.-This conglomerate gland here differs chiefly from that in birds by the progressive development of a part more or less distinct from that which is lodged within the loop or fold of the duodenum: such added part may be represented by that freely projecting end of a fold of the bird's duodenal pancreas (vol. ii. p. 175, fig. 87, q), which stretches towards the spleen, but there is no transverse part of the gland extending at right angles from the duodenal portion, like that which forms the splenic or transverse pancreas in the Mammalian class, and which ultimately becomes the main part or body of the gland in them. In most Mammals the pancreas is of a pale flesh colour, but usually less pink or of less decided tint than in birds: it is firmer in texture, and shows more plainly its conglomerate

structure.

The pancreas in the Ornithorhynchus is a thin, somewhat ramified gland bent upon itself; the left and larger portion descends by the side of the left lobe of the spleen. The pancreas is thicker in the Echidna, and enlarges considerably towards the duodenum. The principal difference occurs in the place of termination of the pancreatic duct, which, in the Ornithorhynchus, joins the ductus choledochus, but in the Echidna terminates separately in the duodenum and nearer the pylorus than does the ductus choledochus. The arrangement of the hepatic and pancreatic ducts is thus conformable to the Mammalian type, and the Orni

1

CXXII. pl. xi. fig. 11.

2 Well explained in CLVIII", p. 185.

thorhynchus, in the place of the junction of these ducts near the commencement of the ductus choledochus, manifests its affinity to the Marsupials. In these the pancreas extends as usual from the duodenum to the spleen, behind the stomach; it is characterised by a process sent off at right angles, or nearly so, to the main lobe at or near its left extremity. Small and thin processes branch out into the duodenal mesentery (in a Phalanger); and similar but still more numerous processes, in the peritoneal attaching, or omental, fold to the left, give the organ a dendritic appearance in the Kangaroo; but the splenic process seems to be constant. The pancreatic duct usually opens into the glandular dilatation of the ductus choledochus, and the secretions enter the intestine further from the pylorus than usual.

The same low type of gland prevails in the Rodentia, and is well shown by Hyde Salter in the rat (Mus decumanus, fig. 380, the main part of the gland being that which extends from the end of the duodenal fold to the left into the gastrosplenic omentum, o, where it ramifies: the chief part of the duodenal pancreas follows the curve of the gut, but ramifies in its wide messentery, d. In the Cavy, where the duodenal loop is longer and narrower than in the Rat, the included portion of pancreas reminds one of the disposition of that in the Bird. In the Capybara the resemblance is less because the duodenum is shorter, and the corresponding part of the pancreas is small: the transverse and larger part of the gland is also more compact than in most Rodents. In the Porcupine the duct of the larger part of the pancreas enters the duodenum far from the pylorus. In the Beaver the pancreas is of considerable extent, measuring in length nearly 2 feet, and following the course of the duodenum down to the iliac region and up again as far as the umbilical, being attached to the intestine by a process of mesentery: it is thin and narrow, and has one small branch or process lying parallel with its body where it passes behind the liver, and a few others at the curvature of the duodenum. Its duct, somewhat larger than a crow-quill, enters the small intestine at the extremity of the gland, 1 foot and 9 inches from the pylorus, and 1 foot and 6 inches from the termination of the ductus choledochus.2 This is the extreme of distance from the pylorus and bile-conduits of the entry of the pancreatic secretion into the intestinal tract, which has been observed in Mammals: the character prevails in the Rodent order, and Physiologists have availed themselves of it in the Rabbit in

experimental research on the action of the bile in the intestine before its admixture with the pancreatic secretion. Most Insec tivora also show the flattened branched form of the pancreas in the broad membranes suspending contiguous organs: it is shown in a large snouted Shrew, in fig. 323, p. In the Hedgehog one of

Pancreas of the Rat (natural size), shown by throwing up the duodenum and duodenal mesentery, OCXXXI.

the duodenal branches hangs freely from the mesentery with an entire investment of peritoneum.'

In the Sloth the left end of the splenic portion of the pancreas has an entire serous coat, and is somewhat loosely suspended from the back of the epiploön: the duodenal portion is narrower. In Myrmecophaga the transverse or splenic portion is long and