KIDNEY. 481 KIDNEY. conveys the urine into the bladder), and enlarges to become the pelvis of the kidney. The jHlvis is lunnel-shuped, with the edges of the large end at- tached to the margin of the sinus, thence turning inward and investing the sheaths of the vessels. The pelvis divides, and then subdivides, the pri- mary segments of the duet being called ealiees. On longitudinal .section, the kidney is seen to be coniposeil of two principal portions: the ex- ternal portion, or cortex, and the more central porliiin, or med'ilhi. The medulla consists i>f frem eight to eighteen conical segments called the pyramids of Malpighi, the apices of which (the papilla") project into the bottom of the sinus and are encircled by the ealiees. and the bases of which are ilirected outward toward the surface and are contiguous to the cortex. Each pyramid is about three-fourths of an inch high, and about two-thirds of an incli across the base, smooth in section, and marked with strife running from base to apex which mark the course of the urinif- erous tubules. The cortex consists of a periph- eral layer, and several processes (columns of Bertini) which pass down between the pyramids of the medulla and reach the sinus. The cortex is somewhat granular, owing to the presence of a Pe/ris DIAHRAM OF KIDNEY. Shon-inK the course of the ui'iiiiferoiis tubules and of the blood-vessels. For coiiveuience, the medulla is represented as greatl.v shortened. af., afferent blood-vessels: ef., efferent blood-vessels: capl.^ caiiillar.v blodd-vessels : s.v., stellate vein ; i-.r., vasae rectse; a., artery; v., vein; g., glomerulus; d., constrict*'*! neck: 6. cap. .Bowman's <Nipsule : p.cproxitnal convoluted tubule; (1., deseendinp: limb ; /., loop; a.s.. ascending limb : ir., irrefjulnr tubule; fl.r., distal convoluted portion; a.r., arched colIertlnK tulnUe; k.c, straight collecting tubule; e.d., excretory ducts or tubes of Bellini. number of very small pyramidal groups of tu- bules, the pyramids of Ferrein. The tubules that carry the urine begin by a numb(>r of spherical capsules in the cortex. From each capsule a narrow tubule passes which becomes wide and convoluted, narrows again as it doubles upon itself and returns, after running down into the subjacent Malpighian pyramid. The narrow loop is called the tube of Henle. It thus runs into the cortex, where it becomes again wide and con- voluted, and finally opens into a straight tube which forms the axis of a pyramid of Ferrein. The straigiit collecting tubes run into the Mal- pighian pyramids, uniting and forming large trunks which terminate in openings in the papil- he of the pyramids, thus emptying their contents into the ealiees. The kidney is very well supplied with blood- vessels. The arteries paas from the point at which they enter the organ at the bottom of the sinus, running up between the Malpighian pyra- mids and subdividing at their bases in cortico- pjn. sra. s.r.a. u fcap. HORIZONTAL SECTION OF THE KIDNEY. Showing the sinus. cap., capsule: p.m.. pyramid of Malpighi; s.r.a., small branch of the renal artery; >.. the infundibulum ; r.a., renal artery: c, cortex; p., a papilla; ir.. ureter; /.c, fatty capsule. medullary arches. These arclies, lying between cortex and medulla, send out arterioles in all directions, tie cortical branches supplying dif- ferent twigs to the glomeruli, which are inclosed in the capsules of Bowman, and ihe medullarj- branches passing inward and f(,rming plexuses around the straight and lo<ipcd tubes of the Mal- pighian pyramids. The efTerent vessels of the glomeruli form a capillary plexus around the uriniierous tubules, and terminate in the renal veins. The leading varieties of the kidneys are as fol- lows: In shape, resulting in the long, globular, or triangular kidney. In size, resulting in one vei- small and one very large kidney. In number, some individuals having only one kid- ney, or rarely three kidneys, the third being in the median line or accompanying one of the others, in the lumbar region. In position, one or both of the kidneys being dislocated. By fu- .'■ion, the two kidneys being joined, and a 'horse- shoe kidney' resulting. In mobility, a laxity of the subperitoneal tissue allowing of the 'floating" of a kidney. Histology. The kidney is a highly differentiated compound tubular gland. It is composed of an external portion, or cortex, and an internal por- tion, or medulla, the latter terminating internally in a number of apices known as papilla-. Each papilla contains the terminations of a system of tubules which, exiending out into the cortex, con- stitute a kidney pyramid or lobule. The division into lobules is readily seen in fo'tal kidneys, and in the kidnevs of certain of the lower animals.
