[544] F. M. Balfour, Comparative Embryology, Vol. II., pp. 600-603 [the original edition].
[545] F. M. Balfour, “On the Origin and History of the Urinogenital Organs of Vertebrates,” Journ. of Anat. and Phys., Vol. X., 1876 [This edition, No. VII].
[546] F. M. Balfour, Comparative Embryology, Vol. II., p. 605 [the original edition].
The Alimentary Canal and its Appendages.
I.—Anatomy.
Agassiz (No. 2) gives a short description with a figure of the viscera of Lepidosteus as a whole. Van der Hœven has also given a figure of them in his memoir on the air-bladder of this form (No. 8), and Johannes Müller first detected the spiral valve and gave a short account of it in his memoir (No. 13). Stannius, again, makes several references to the viscera of Lepidosteus in his anatomy of the Vertebrata, and throws some doubt on Müller's determination of the spiral valve.
The following description refers to a female Lepidosteus of 100.5 centims. (Plate 40, fig. 66).
With reference to the mouth and pharynx, we have nothing special to remark. Immediately behind the pharynx there comes an elongated tube, which is not divisible into stomach and œsophagus, and may be called the stomach (st.). It is about 44.6 centims. long, and gradually narrows from the middle towards the hinder or pyloric extremity. It runs straight backwards for the greater part of its length, the last 3.8 centims., however, taking a sudden bend forwards. For about half its length the walls are thin, and the mucous membrane is smooth; in the posterior half the walls are thick, and the mucous membrane is raised into numerous longitudinal ridges. The peculiar glandular structure of the epithelium of this part in the embryo is shewn in Plate 40, fig. 62 (st.). Its opening into the duodenum is provided with a very distinct pyloric valve (py.). This valve projects into a kind of chamber, freely communicating with the duodenum, and containing four large pits (c´), into each of which a group of pyloric cæca opens. These cæca form a fairly compact gland (c.) about 6.5 centims. long, which overlaps the stomach anteriorly, and the duodenum posteriorly.
Close to the pyloric valve, on its right side, is a small papilla, on the apex of which the bile duct opens (b.d´).
A small, apparently glandular, mass closely connected with the bile duct, in the position in which we have seen the pancreas in the larva (Plate 40, figs. 62 and 63, p.), is almost certainly a rudimentary pancreas, like that of many Teleostei; but its preservation was too bad for histological examination. We believe that the pancreas of Lepidosteus has hitherto been overlooked.