_Fish_ also possess several (up to four) embryonic pancreatic outgrowths.
Recently in human embryos of 4.9 mm. cervico-coccygeal measure three pancreatic outgrowths have been observed, all entirely distinct from each other, one dorsal, budding from the epithelium of the primitive duodenum and two ventral, proceeding from the grooved gutter which represents the primitive ductus choledochus at this period. In embryos of from 6 to 10 mm. the two ventral outgrowths have already fused, hence only two buds, a single ventral and a dorsal, are now encountered.[4]
[4] Iankelowitz, Arch. f. Mikr. Anat., Bd. 46, 1895.
These observations place the development of the human pancreas in line with the triple pancreatic outgrowths, two ventral and one dorsal characteristic of the majority of the lower vertebrates, which have been hitherto carefully examined. The ventral or distal bud is probably double in the majority of vertebrates. The two segments fuse, however, so early that the derivation of the pancreas from a double outgrowth, as described above for the human embryo, practically obtains. In forms in which the adult gland presents a number of separate openings into the duodenum (cf. p. 118), the development would probably show multiple embryonic outgrowths from the intestinal hypoblast.
In any case the dorsal pancreatic bud appears to have developed in the vertebrate series before the ventral outgrowth and to be hence phylogenetically the older structure.
With the exception of _Amphioxus_ and probably also of the _Cyclostomata_, the gland appears to be present in all vertebrates, varying, however, much in size, shape and relation to the intestinal tube. Usually it appears as an elongated, flattened, more or less distinctly lobulated organ, in close apposition to the duodenum between the layers of the mesoduodenum. In all forms in which the gland is found it is connected with the post-gastric intestine and marks the beginning of the midgut. In structure the gland is usually acinous, resembling the salivary glands. It is well developed in the selachians, forming a triangular body connected with the beginning of the midgut (Fig. 202). In some instances the gland elements do not extend beyond the intestine itself, but remain imbedded in the wall of the midgut, as in _Protopterus_. In certain adult teleosts the pancreas is surrounded by the liver (Fig. 196), in others it does not appear as a compact gland but is distributed in the form of finely scattered lobules throughout the mesentery between the two layers of this membrane. On account of this concealed position of the gland it was formerly believed that the adult teleosts did not possess a pancreas. The pyloric cæca (cf. p. 119) found in these forms were consequently considered to be homologous with the pancreas of the higher vertebrates.