1246 



UROGENITAL SYSTEM 



the kidney corresponds with the region where a hiatus diaphragmaticus between the costal and 

 lumbar portions of the muscle may occur and if this be pronounced the upper part of the pos- 

 terior surface of the kidney may come into more or less direct relations to the pleura (fig. 1008). 



Just as there may be variation in the position of the kidneys, so too there may be con- 

 siderable variation in the extent to which they are in relation to the various structures men- 

 tioned above. And this is especially true as regards their relations to the colons; for if the 

 kidneys were lower than usual they might lie entirely beneath the line of attachment of the 

 transverse mesocolon and thus have no direct relations with either colon, or on the other hand 

 either the ascending or descending colon, or both, may be provided with a mesentery, whereby 

 they would be removed from direct contact with the kidney. 



Structure. — A section thi'ough the kidney shows its substance to be composed of an ex- 

 ternal or cortical [substantia corticalis] and an internal or medullary portion [substantia 

 meduUaris] (fig. 1010). The medulla consists of a variable number (eight to eighteen) of 

 conical segments termed renal pyramids [pyramides renales (Malpighii)], the apices of which 

 project into the bottom of the sinus (fig. 1006) and are received into the primary segments 

 (calyces) of the pelvis, while their bases are turned toward the surface, but are separated from 

 it and from each other by the cortex. The pyramids are smooth and somewhat ghstening in 

 section and are marked with delicate striae which converge from the base to the apex and in- 

 dicate the course of the renal tubules. The blunted apex, or papilla, of each pyramid, either 

 singly or blended with one or even two of its fellows, is embraced by a calyx (fig. 1006), and, if 

 examined with a hand-lens, will be seen to present a variable number (twelve to eighty) of 

 minute apertures, the foramina papillaria, which represent the terminations of as many 

 papillary ducts (of Bellini) through which the secretion escapes into the pelvis. 



Fig. 1010. — Horizontal Section of Kidney showing the Sinus. 



Pyramid of 



Malpighi 



Column of Berlin 



Interlobar 

 artery 



Artery 



Capsule 



Cortex with pyrami ds / /j^ 

 of Ferrein 



Branch of artery 



Ureter 



Irregular branch of artery 

 Portion of 

 fatty capsule 



The cortex may be regarded as composed of two portions, (1) a peripheral layer, the cor- 

 tex proper, which is about 12 mm. in thickness and extends from the fibrous capsule to 

 the bases of the pyramids, and (2) processes termed renal columns [columnaj renales (Bertini)] 

 which dip inward between the pyramids to reach the bottom of the sinus (fig. 1010). In 

 section the cortex is somewhat granular in aspect, and when examined closely shows a diiferen- 

 tiation into a luunher of imperfectly separated portions termed cortical lobules [lobuli corticales]. 

 Each of these is composed of a convoluted portion [pars convoluta], surrounding an axial radiate 

 portion (pyramid of Ferrein) li)ars radiata (processus Ferreini)]. The latter consists of a group 

 of tubules which extend from the cortex into the base of one of the medullary pyramids, whence 

 it is also termed a medullary ray; and each medullary pyramid is formed from the rays of a 

 number of cortical l<)l)ules, these structures, therefore, greatly exceeding the pyramids in 

 number. 



Renal tubules (fig. 1011). — The structure described above is the result of the arrange- 

 ment of the renal tubules, which constitute the essential imits of the kidney. Each of these com- 

 mences in a Hph(!rical glomerular capsule (fig. 101 1), one wall of which is invaginated by a small 

 glomcruluH of blooil-v(!ss('ls, the conibination of glomerulus and capsule forming what is termed 

 a renal (Malpighian) corpuscle. TIk^.sc! corpuschis are situated in the convoluted portions of 

 the cortical lobules, anil from (sacli of t hem there arises by a narrow neck a tubule, which quickly 

 becomes wide and convoluted, this portion being termed the first convoluted tubule. This 

 enters a medullary ray, where it narrows again and descends as a straight tubule, the de- 

 scending limb of Henle's loop, into the subJ!ic(!nt medullary pyramid, and, turning upon itself, 

 forming the loop of Henle, ascends to the cortex, where it again beconu^s \w'uh\ aiul contorted, 

 forming the second convoluted tubule. This again lies in the convoluted portion of the cortical 

 lobule, and, becoming narrower, opc^ns with otlier similar tubules into a straight or collecting 



