254. The Kidneys. The kidneys are two important organs in the abdomen, one on each side of the spine. They are of a reddish-brown color, and are enveloped by a transparent capsule made up of a fold of the peritoneum. Embedded in fat, the kidneys lie between the upper lumbar vertebræ, and the crest of the hip bone. The liver is above the right kidney, and the spleen above the left, while both lie close against the rear wall of the abdomen, with the intestines in front of them. The human kidneys, though somewhat larger, are exactly of the same shape, color, and general appearance as those of the sheep, so commonly seen in the markets. The kidneys are about four inches long, two inches across, one inch thick, and weigh from 41/2 to 51/2 ounces each. The hollow or concave side of the kidneys is turned inwards, and the deep fissure of this side, known as the hilus, widens out to form the pelvis. Through the hilus the renal artery passes into each kidney, and from each hilus passes outwards the renal vein, a branch of the inferior vena cava. A tube, called the ureter, passes out from the concave border of each kidney, turns downwards, and enters the bladder in the basin of the pelvis. This tube is from 12 to 14 inches long, about as large as a goose quill, and conveys the secretion of the kidneys to the bladder. 255. Structure of the Kidneys. The pelvis is surrounded by reddish cones, about twelve in number, projecting into it, called the pyramids of Malpighi. The apices of these cones, known as the _papillæ_, are crowded with minute openings, the mouths of the uriniferous tubules, which form the substance of the kidney. These lie parallel in the medullary or central structure, but On reaching the cortical or outer layer, they wind about and interlace, ending, at last, in dilated closed sacs called Malpighian capsules. Illustration: Fig. 108.—Vertical Section of the Kidney. A, pyramids of Malpighi; B, apices, or papillæ, of the pyramids, surrounded by subdivisions of the pelvis known as cups or calices; C, pelvis of the kidney; D, upper end of ureter.