The Spleen is about 5 inches long and 3 inches broad. It may be compared in shape to a thick pancake, which, instead of being circular, is roughly triangular in outline, while its visceral surface presents marked indentations caused by pressure of adjacent organs. It is placed far back in the upper portion of the abdominal cavity, its long axis corresponding in direction to the posterior portion of the tenth rib, while its parietal surface is moulded to the back part of the diaphragm, by which, together with pleura and thin basal margin of lung, it is separated from the ninth, tenth, and eleventh ribs. The apex reaches a point 1 inch from the spine. The anterior basal angle is the most anterior part, but does not present normally beyond the costal margin. The notch of the spleen lies above this angle on the anterior margin. The visceral surface presents three impressions-anterior, posterior, and inferior. Anteriorly a deep concavity corresponds to the fundus of the stomach, arid near the posterior part of this depression is the hilum at which the vessels enter. Behind the gastric depression is the renal depression, formed by the anterior surface of the kidney ; while lying under these two is the intestinal impression, formed by the splenic flexure of the colon. In the neighbourhood of -the spleen accessory masses of splenic tissue are not infrequently found (lienculi). The spleen is almost enveloped in peritoneum, the peritoneum passing from the hilum to the anterior surface of the kidney, forming the lieno-renal ligament; and to the fundus of the stomach, forming the gastvo-splenic omentum. Under the peritoneal covering the spleen possesses a tough fibrous capsule, containing both elastic and involuntary muscular fibres. While distensible, this capsule is also contractile, and may account for arrest of haemorrhage in punctured or gunshot wounds of the spleen. The blood is conveyed by the splenic artery, the largest branch of the cceliac axis, which runs along the upper border of the pancreas ; passes between the layers of the lieno-renal ligament ; breaks up into several branches, and so enters the hilus after supplying branches to the stomach. The splenic vein joins the superior mesenteric behind the head of the pancreas to form the portal vein.

The nerve-supply is the splenic plexus, derived from the coeliac of the solar plexus. There are no lymphatics in the spleen, but some are present in the capsule. The normal position of the spleen is indicated by a line running obliquely downwards and forwards from a point 1½ inches in front of the ninth dorsal spine to a point on the tenth rib at the level of the first lumbar spine, encircled by an oval 3 inches in transverse diameter. Owing to the intervention of the lung between the spleen and chest wall, it is practically impossible to outline its limits. Normally, the spleen does not project beyond the ribs, but, when enlarged, the anterior basal angle projects, and then it is generally possible to detect one or more notches on the anterior border, which serve to distinguish splenic from other enlargements in the same region.

Pathological enlargement of the spleen is seen in various fevers, and chronically in leucocythaemia, Hodgkin's disease, malaria (ague cake), etc. In the latter the organ is extremely easily ruptured, fatal haemorrhage frequently following the accident. In some cases the enlargement is enormous, the spleen occupying the greater part of the abdomen. The spleen may be punctured by fractured ribs, but not infrequently the spleen is ruptured, whereas, owing to their elasticity, the ribs escape fracture. As the spleen is very vascular, enormous hemorrhage generally occurs, the abdomen being filled with blood, and death generally resulting. In some cases, however, the ruptured spleen has been removed, and the bleeding vessels ligatured, with excellent results. As the splenic artery is an end artery, infarctions not infrequently occur in the spleen, from emboli being lodged, and if these are septic, abscesses may arise. These are generally multiple and peripheral. A large single abscess of the spleen is rare. Particularly in females, and associated with general displacement of the viscera, the spleen may be found displaced, and possessing an elongated pedicle, which permits of considerable movement, the spleen sometimes reaching the pelvis (wandering spleen). In such cases the spleen may be restored and fixed by sutures (splenopexy), or may be removed (splenectomy).