This section is from the book "Applied Anatomy: The Construction Of The Human Body", by Gwilym G. Davis. Also available from Amazon: Applied anatomy: The construction of the human body.
The spleen lies high up in the left posterior corner of the abdomen in contact with the diaphragm. It follows the direction of the tenth rib, being covered by the ninth, tenth, and eleventh ribs and extending from a point 4.5 to 5 cm. (1 1/2 to 2 in.) external to the median line posteriorly to the midaxillary line anteriorly. Its upper end is opposite the tenth dorsal vertebra, or ninth spine (see Fig. 433).
It has four surfaces: a posterior one, which lies in contact with the diaphragm; an anterior one toward the stomach; an inferior small one, resting on the splenic flexure of the colon; and an internal one, in contact with the left kidney at its upper anterior portion. The hilum is on its anterior or gastric surface and posterior to it is a depression in which is lodged the tail of the pancreas.
The spleen is covered with peritoneum except at the hilum, which is on its anterior surface; here two ligaments are given off - a posterior one, the lienorenal, going from the spleen to the kidney and containing the blood-vessels, and an anterior one, the gastrosplenic (also called omentum) going to the stomach. The lienophrenic ligament (suspensory ligament) runs from the left crus of the diaphragm to the upper inner edge of the spleen and blends with the two former ligaments. These three ligaments form a pedicle from which the spleen swings, and it is by their stretching that the spleen at times descends and is detected below the edge of the ribs. A fourth ligament, the phrenocolic (costocolic) runs from the diaphragm opposite the tenth and eleventh ribs to the splenic flexure of the colon. The upper surface of the colon is concave, forming a fossa (splenic fossa) in which the spleen rests and which, of course, aids in supporting it.
The spleen is enlarged in many diseases, such as malaria, leukaemia, typhoid fever, and others. This enlargement is to be detected by palpation and percussion. The normal spleen lies under the ribs, therefore it can be palpated only when it enlarges and projects beyond the costal margin or when its pedicle (ligaments) becomes stretched and allows it to wander down. Normal percussion dulness extends anteriorly to the midaxillary line; posteriorly it merges into the kidney dulness and cannot be limited. From above down the dulness would be from the ninth to the eleventh rib in the posterior axillary line.
-The upper portion of the spleen rises as high as the tenth dorsal vertebra or ninth spine; as the lung posteriorly descends at least one vertebra lower and the pleura still another lower, it follows that a penetrating wound entering the ninth costal interspace in the line of the angle of the scapula would wound first the pleura, then the lung, then the diaphragm, then the spleen, and finally the stomach. If it entered one interspace below - the tenth - it would open the pleural cavity but would probably escape the edge of the lung.