The stomach is much thicker, and naturally more muscular, than either the oesophagus or intestines, and presents the ap- pearance of an elongated transverse canal doubled upon itself. Neither the mucous membrane of the stomach nor of the intestines is arranged in folds, but both are finely and beautifully reticulated over their entire surfaces. The lower portion of the gullet, how- ever, is longitudinally plicated, apparently from the contraction of its muscular covering.
The heart possesses two fleshy auricles, and, on casual external inspection, when in motion, apparently contains also two ventricles ; but on opening it, the deception is readily accounted for by a strong muscular septum that partially divides the common ventricle. Four arterial orifices, each guarded by valves will likewise be noted, three of which communicate with the cavity on the left side of the septum, while the fourth, that of the pulmonary artery, is upon the right. The venæ cavæ pulsate simultaneously with the common ventricle, and alternately with the auricles.
Two flat lobes, connected merely by a pair of narrow transverse bands, constitute the liver. To the right lobe is appended the gall- bladder, a mere cyst, which is not received into a fissure or groove, but lies externally enclosed by a sac, which is apparently a prolification of the peritoneal hepatic membrane. The spleen is a cylindrical organ, its length exceeding by about three times its transverse diameter, and varying little in proportion to the different sizes of adult specimens, averaging upwards of an inch — from an inch and a quarter to an inch and a half — in length by one half to three-fourths of an inch in diameter. The pancreas is closely attached to the duodenum, and in the largest female specimens exceeds four inches in length, being of narrow flattened form : in a large male it was but two and one-eighth inches, and a trifle broader and more rounded in proportion.
The kidneys are composed of numerous lobes closely over- lapping each other; the ureters terminate in the cloaca at from a half to three-fourths of an inch from the orifice of the bladder, being attached to the nipple-like processes of the oviduct in the female (precisely as described by Owen as occurring in Platypus anatinus), and in the male upon the vas-deferens, the latter likewise forming small but markedly distinct papillæ. The bladder presents a uniform oval outline, and is very obviously muscular, much more so than the Emydidæ and
