Spleen (Gr. σπλήν), the largest of the vascular or ductless glands, whose probable function is subsidiary to the process of sanguification. It is situated in the left hypochondriac region, below the diaphragm, above the descending colon, between the cartilages of the false ribs and the cardiac extremity of the stomach, to which it is united by short vessels. It is in health from 4 to 5 in. long, and 1½ in. thick, of an elongated flattened form, and about 6 oz. in weight; on the inner surface is a longitudinal groove in which are the blood vessels, posteriorly resting on the vertebral column; below, it is in relation with the left kidney and capsule, and with the pancreas behind. It is soft and spongy, and dusky red.

A portion of the Splenic Artery, its ramifications being studded with Malpighian corpuscles.

A portion of the Splenic Artery, its ramifications being studded with Malpighian corpuscles (from the dog). (Magnified 10 diameters).

Its external surface is covered with the peritoneum; beneath this is a coat of white fibrous tissue with some elastic fibres, from the inner surface of which extends through the entire organ a network of fibrous bands and threads, the trabecular tissue. The splenic artery comes from the coeliac axis, the trunks not anastomosing, but subdividing like the branches of a tree, to which the Malpighian corpuscles are attached as fruits on short peduncles, and ending generally in capillaries with very thin walls, passing in every direction through the organ and into the interior of the corpuscles. The veins are branched like the arteries, have no valves, and their principal stem is one of the trunks of the vena portae; the nerves form the splenic plexus, and proceed from the solar plexus of the great sympathetic; the lymphatics are few and superficial. The parenchyma consists of a homogeneous mass of colorless nucleated corpuscles and cells imbedded in a granular plasma. The splenic corpuscles, or Malpighian bodies of the spleen, are whitish spherical bodies, about 1/70 of an inch in diameter, attached to the smaller ramifications of the splenic artery.

Each corpuscle consists of a closed sac or capsule, containing in its interior a viscid semi-solid mass of cells, cell nuclei, and homogeneous substance. Each Malpighian body is covered with a network of capillary blood vessels; and small blood vessels also penetrate into its interior, through the investing capsule, and form a vascular capillary plexus in the substance of the body itself. - The precise details of the function of the spleen are unknown. It belongs to the class of "ductless glands," that is, of organs having a glandular texture but no outlet or duct, and not supplying any distinct secretion like those of the glands proper. Their purpose undoubtedly is to effect some necessary change in the blood itself, producing in their glandular tissue some substance which is appropriated and carried away by the blood vessels distributed to them. Thus the veins of these organs are supposed to serve as their excretory ducts. The spleen, though so large, is not directly essential to life, and has been several times removed in the lower animals without an immediately fatal result.

It is liable to acute and chronic enlargements in various forms of typhoid and intermittent fevers, and is sometimes excessively enlarged and solidified in the strumous diseases of infancy and childhood.