The Alimentary Canal

This part of vertebrate organization always exhibits a differentiation into mouth, pharynx, oesophagus, stomach, and intestine; and the last has always a median, or nearly median, aperture on the ventral surface of the body. It may open by itself; or into a cloaca, or chamber common to it, the urinary and the genital organs.

The intestine is generally distinguishable into small and large; and, at the junction of the two, one or two coeca are frequently developed from the former.

The stomach and intestine are invested by a peritoneal membrane, and connected, by mesogastric and mesenteric folds of that membrane, with the median dorsal wall of the abdominal cavity. Glands appertaining to the lymphatic system frequently abound in the mesenteric folds, and a highly-vascular gland of this system, the spleen, is always (except in Amphioxus, Myxine, and the Leptocephalidae) developed in close proximity to the stomach. A pancreatic gland very generally pours its secretion into the anterior end of the intestine. Salivary glands very commonly open into the mouth; and, in the higher Vertebrata, anal glands are not unusually developed in connection with the termination of the rectum.

The structures connected with the alimentary canal of vertebrate animals, which are most characteristic and peculiar, are the liver and the teeth.