The pancreas, an organ functionating as a gland with an internal secretion and by pouring a digestive juice into the duodenum, remains a structure of constant anatomy throughout the zoological classes under discussion in that it is composed of compound racemose lobules whose outlets join to form large discharging ducts, and of interstitial bodies, the islands of Langerhans, without connection with the secreting acini but having some relation with the blood and lymph vessels. The organ originates embryologically by sprouts from the side of the primitive gut just below the part destined to be stomach, and from an outbudding of the common biliary duct. These two sprouts or pouches combine to form one organ, but this does not necessarily effect a union between their lumina. In some birds and mammals (Accipitres and some Ungulata) the lobes of the pancreas remain distinct during life, and the discharging tubules seem to empty only their respective lobes. However, there is no uniformity in the matter, and indeed the anatomy of the ducts is subject to very great variation despite the rather similar beginnings of the organ. Those who are interested in this point may consult Beddard,[25] Letulle and Nathan-Larrier,[26] and Opie[27]; there will be given in the following pages the average findings of anatomy of the gland body and of its ducts. The region of the pancreas in lower animals, especially those which travel constantly on four feet, is one of great activity, and the organs are more freely movable than in the human being. The only exception to the latter part of this statement may possibly be found in the cats and dogs, in which there are firmer attachments of the duodenum and pancreas to the vertebral column and the liver; this is brought about by the short gastrohepatic omentum and the abrupt curvature of the duodenum toward the back, under the mesenteric stalk. In the Ungulata and Marsupialia and in some Rodentia, the pyloric, duodenal, and pancreatic attachments are relatively loose, and torsion of the pylorus seems to be allowed for, since in these animals great distention of the stomach is the rule. Among the Aves the anatomy is wholly different. The birds have no attachment of the duodenum and pancreas to the posterior abdominal wall, except indirectly through a narrow strip comparable to the gastrohepatic omentum, one division of which passes to the beginning of the duodenum, the other to its end, and by a thin tail of pancreas which goes toward the spleen. The bulk of the pancreas lies in the U made by the long free duodenal loop, the two organs being covered by the serous membranes forming the middle abdominal sac. It will be seen from the foregoing that the movability of the pancreas is considerable—a highly necessary provision, because the stomach and duodenum are also movable and subject to distention by food and alteration of position during flight.