A closely similar if not identical species from the American coast of the North Pacific has been described under the name of _Phocæna vomerina_, and another from the mouth of the Rio de la Plata as _P. spinipennis_. [Illustration: FIG. 94.—Diagrammatic section of the stomach of the Porpoise. _a_, Œsophagus; _b_, left, or cardiac, compartment; _c_, middle compartment; _d_ and _e_, the two divisions of the right, or pyloric, compartment; _f_, pylorus; _g_, duodenum, dilated at its commencement; _h_, biliary duct.] The stomach of the Porpoise (Fig. 94) may be taken as a typical example of this organ in the Cetacea. The first and by far the largest compartment (_b_) may be regarded as a kind of crop, or dilatation of the large œsophagus (_a_). It is lined by a thick white epithelium, which ceases abruptly at the entrance into the next cavity. It corresponds to the cardiac compartment of the stomach in the Ungulates and certain Rodents; but, although its walls do not appear to contain peptic glands, its contents undergo partial digestion—probably caused by the regurgitation into it of the secretions of the second, or true digestive compartment (_c_). This, which is much smaller than the first, has very thick walls, the mucous membrane being filled with numerous tubular glands. The surface of this membrane is smooth and soft, being thrown into numerous folds, which in this genus are arranged in a very peculiar and characteristic manner, so as to form a series of prominent longitudinal ridges, each of which sends off short lateral ridges at right angles to itself, which interdigitate with those proceeding from the next longitudinal ridge. The remainder of the stomach (_d_ to _f_) may be compared to the pyloric antrum of the stomach of ordinary mammals. It is elongated, cylindrical, and intestiniform, with a smooth lining membrane, sharply bent upon itself, and terminating in a very small circular pyloric aperture (_f_). In the Porpoise the commencement of this cavity is constricted off from the remainder, so as to form a small globular sac. In most Dolphins (as _Tursiops_, _Globicephalus_, and _Grampus_) there are two such small sacs of very similar size and form, communicating by circular pylorus-like apertures; and in _Hyperoödon_ the whole compartment is divided by a series of constrictions into as many as seven separate cavities, which have been regarded as distinct stomachs. Immediately beyond the pylorus the duodenum has a globular dilatation, as in the camels and some other Ungulates, into the lower end of which the biliary duct (_h_) enters.