With Figure 2.
The stomach, which in these animals, like the paunch of Ruminants, is never found empty after they begin to eat solid food, has been removed, with the exception of a little more than an inch of its pyloric end, a. As in nearly all Vertebrata, with the exception of the Ophidians, the terminal segment of the digestive tract, h to k, comes into close juxtaposition with this portion of the stomach and the duodenum 1 As noteworthy points more or less distinctive of the Rabbit may be enumerated, firstly, the great distance, a foot or even as much as twenty inches from the opening, c, of the bile-duct, at which the pancreatic duct, e, opens into the duodenum secondly, the arrangement of the pancreas in widely-scattered loosely-compacted lobules, spreading all the way from the spleen at f down nearly to the concavity of the loop of duodenum; thirdly, the great length of this loop reminding us of the similarly long duodenum of birds; fourthly, the dilatation, b, at the commencement of the duodenum, an enlargement observable in many phytophagous Rodents, as Lagostomus, and also in the Hyrax, the Llama, and the Bottle-nose whale, Dephinus Dalei1. The descending colon, k, and the loop of duodenum are connected together by a continuous sheet of mesentery, the name therefore of intestinum mesenteriale cannot be confined in these animals, as it has been in others, to the jejunum and ileum; in other words, the colon and duodenum have much greater freedom of movement allowed them by the greater extent of their mesentery than in certain other Mammals.
1 See Cuvier, Lecons d'Anatomie Comparee, ed. 2, 1835, torn. iv. pt. 2, p. 657: 'Dans toutes les classes des vertebres, l'ordre des ophidiens seul excepte, le canal alimentaire a toujours une portion qui repond au gros intestin plus ou moins rapprochee de l'estomac ou du commencement du canal intestinal.' And compare the plates in Rathke's memoir, Ueber den Darmkanal des Fische, 1824, which show that this arrangement exists in most orders of Fishes as well as in air-breathing Vertebrata.
Fig. 2. - (One-half less than natural size.) Duodenum, Pancreas, and Spleen, with portions of Stomach and large Intestine of Rabbit (Lepus cuniculus) in their mutual Relations
a. Pyloric portion of stomach.
b. Dilated commencement of duodenum, receiving c. The bile-duct.
d. Concavity of duodenal loop, within which is contained a large part of e. The pancreas, to the duct of which, opening in the lower portion of the ascending limb of the loop, this line is drawn.
f. Portion of pancreas in relation with the spleen and corresponding to the 'tail' of the organ of anthropotomy.
g. Spleen, with two accessory splenculi.
h. Coil of colon supported by same lamina of peritoneum which attaches the pancreas and duodenum to each other and to the rectum. The letter points to the proximal end of the last coil described by the colon before it joins the rectum.
i. Peyer's patch marking point where duodenum passes into jejunum in a plane anterior to that occupied by the rectum.
j. Left kidney.
k. Rectum containing scybala.
Between the portion of the colon, shown here in section at h, and the segment next the caecum, shown similarly in Preparation 7 and in Fig. 3 at f, certain coils not shown in either figure intervene. A part of these coils corresponds to the spirally-coiled portion 2 of the colon of the Artio-dactyla, but this correspondence is more plainly demonstrable in the Guinea Pig than in the Rabbit.
Professor Claude Bernard has, in the Supplement aux Comptes Rendus, tom, i. Pl. 3-4, Fig. 5, 1856, figured a pancreas of the Rabbit with a second, which is a much smaller, duct opening into the bile-duct just before its entrance into the intestine. On Pl. 7-8 l. c. he has figured the same organ from a Rabbit in which only the single duct figured here was present, and in which oily matter had been mixed with the animal's food. In this case it is only distally to the point of entrance of the duct that the lacteals are seen to be filled with white fluid and to have absorbed the oily matter ingested. This fact has been explained by Bidder and Schmidt, Die Verdauungss'afte und der StorTwechsel, p. 256, 1852, as being due to the oily matter having been absorbed in the proximal segments of the duodenum, and having been also passed through the lacteal vessels in connection with them, and so having disappeared from view in the period of from five to six hours which they suppose to have been allowed to elapse between the ingestion of the oily matter and the examination of the duodenum.
Bernard's views were controverted by other physiologists (see Schiff, Moleschott's Untersuchungen, ii. p. 345, 1857, and Krause, l. c. p. 163), but in answer, Bernard appealed to the existence firstly of a second duct in the situation above specified, and secondly of certain accessory pancreatic glands either sessile upon or with ducts opening into the bile-duct (see figures, pp. 350-351, Lecons sur les proprie'te's physiologiques des Liquides de l'organisme, 1857). The second duct, however, of the pancreas in the Rabbit, though such an accessory duct does exist in several Ungulata, several Carnivora, the Elephant, and the Beaver, has been allowed by Bernard himself not to be constantly present (see Comptes Rendus, l. c. p. 390, and Lecons de Physiologie Expe'rimentale, 1856, ii. p. 271, in which last work it is best described as 'petit conduit pancre'atique exceptionnel venant s'ouvrir dans le canal chole'doque'); and Krause, l. c., suggests that a branch of the arteria gastro-epiploica dextra has been taken in an uninjected preparation for a duct.
As regards the smaller accessory pancreatic glandules in connection with the bile-duct, Donders and Kuhne have remarked that they would be quantitatively inadequate to account for the emulsification of fatty matters which has sometimes been observed to have taken place in the duodenum above the opening of the pancreatic duct. On the whole, however, it seems that though some emulsification is effected independently of the pancreas, the appearances figured by Bernard, Comptes Rendus, l. c., are so constant as to show that the process is very greatly helped by the secretion in question. For good summaries of the whole question, see Kuhne, Lehrbuch der Physiologischen Chemie, 1868, pp. 131-133, and Foster's Text-Book of Physiology, 4th ed. 1883, p. 295 (ed.- 3, p. 279). The existence in certain animals of more than a single duct to the pancreas was first pointed out by De Graaf, in his Tractatus Anatomico-medicus de succi pancreatici natura et usu, pp. 16-17, 1671. The duplex and triplex ductus, however, are illustrated by him only by instances from Birds; amongst Mammals he only records the presence of a second smaller duct as having been occasionally found in Man and the Dog. See also Nuhn, Lehrbuch der Vergleichenden Ana-tomie, pp. 50-51, 1878.
1 See Owen, P. Z. S. 1839, P. I76. and Hunterian Catalogue, vol. i. 566 B.
2 For a figure showing the spirally-coiled portion of the colon, the caecum, and the small intestine of an Artiodactyle, see Dr. Cobbold, Cyclopaedia of Anatomy and Physiology, vol. v. art. 'Ruminantia,' Fig. 361, p. 538. For several showing similar arrangements in Rodentia, see Pallas, Novae Species Glirium, Pl. xvii. 1778.