Fig. 201.—Section of dog’s stomach, and proximal portion of duodenum, with entrance of biliary and pancreatic ducts. (Columbia University Museum, No. 1822.)
In most rodents the pancreatic entrance is placed at some distance from the pylorus. [Fig. 199] shows the arrangement of the parts in the rabbit, in which animal the main distal pancreatic duct empties at a distance of 13″–14″ from the pylorus into the end of the duodenum, which intestine forms a very long loop, while the biliary duct, receiving the smaller proximal pancreatic duct, opens near the pylorus.
In the beaver the smaller proximal duct joins the bile-duct or even enters the duodenum anterior to the bile-duct, nearer the pylorus, while the distal larger pancreatic duct opens into the intestine 16″–18″ behind the biliary duct. Of the two ducts found in the dog ([Fig. 200]) the smaller proximal either joins the bile-duct or opens into the intestine close to it, 1″–1½″ beyond the pylorus. The larger distal duct opens into the duodenum 1″–1½″ behind the biliary duct. Fig. 201 shows the dog’s stomach and proximal portion of the duodenum in section. The proximal smaller pancreatic duct here joins the biliary duct, and opens with it by a single orifice into the duodenum. The distal larger pancreatic duct opens independently into the intestine further caudad.
The parts in Hyæna present a similar arrangement.
Bernard always found two pancreatic ducts in the cat, one large principal duct and a second smaller accessory duct. Of these, the one situated nearest to the pylorus always united with the bile-duct. The pancreatic duct thus joining the bile-duct was sometimes the main duct, sometimes the accessory smaller duct.
Since the main function of the pancreatic juice is the conversion of starch into sugar, the gland appears better developed in general in herbivora than in carnivora, without, however, disappearing in the latter. In fact it is of considerable size in the carnivora, because the secretion also acts on the albuminous food substances and, though to a lesser degree, on the fats.
PYLORIC CÆCA OR APPENDICES.
In the Cyclostomata and Selachians the intestinal canal is in the main free from cæcal appendages, while a large portion of the tube is provided with a special fold of the mucous membrane which projects into the lumen of the gut (spiral valve). [Fig. 43] shows the straight intestinal tract with the spiral valve of the longer distal segment in a cyclostome, Petromyzon marinus or lamprey. In [Figs. 202] and [203] the selachian (shark) intestine is represented in two examples, while the similar spiral valve in a Dipnœan or lung fish, Ceratodus, is seen in [Fig. 204].
Fig. 202.—Alimentary tract with spleen and pancreas of Squalus acanthias, the dog-fish. (Columbia University Museum, No. 1405.)