aia 
1086 UROGENITAL SYSTEM. 
are termed the medullary pyramids (pyraimides renales), and together constitute the 
medulla (substantia medullaris) of the kidney. The bases of “the pyramids do not 
reach the surface of the kidney, but are separ- 
aes ated from it by a thin layer of kidney substance 
ee” called cortex, or the cortical part of the kidney 
\aree (Substantia corticalis). The cortical substance 
JeriPrese’’ not only covers over the bases of the pyramids, 
but also sends in ee aie called columns 
of Bertin (column renales), between the pyra- 
mids, towards the sinus. The medullary part 
of the kidney exhibits in section a striated 
BiG. 732.—SMALL PORTION OF THE WALL appearance, while the cortical part is more 
OF THE KIDNEY SINUS. ™ 
eranular and usually different in colour. The 
outer part of each pyramid, or the intermediate zone (basis pyramidis), as it is 
termed, appears in section to be composed of alternate dark and light streaks, 
while the inner or papillary part, which is of a lighter colour, is more uniformly 
and faimtly striated. 
In sections of the kidney the larger blood-vessels are seen, after they have 
entered the kidney substance, to le between the pyramids; some of their main 
branches are also visible passing across the bases of the pyramids. 
Papilla 
In the foetus and young child, and sometimes even in the adult, the surface of the 
kidney is marked by a “number of grooves dividing it into polygonal areas. These repre- 
sent the lobes (lobi renales) of which the kidney is originally composed. Each lobe 
corresponds to one pyramid with its surrounding cortical substance. 
An examination, with an ordinary pocket lens, of a section through the kidney 
shows that the lighter strie of the intermediate zone are continued into the cortex. 
As they pass through the cortex towards the surface of the kidney they become 
less distinct, and appear as separate ray-like prolongations carried outward from 
the bases of the pyramids. These parts of the cortex, which appear in this way to 
be continuations of the medulla, are called medullary rays (pars radiata), and the 
portions of kidney cortex which intervene between them form the labyrinth (pars 
FO 3) 
convoluta, Fig. 733) 
Kidney Tubules“‘The substance proper of the kidney is composed of an enormous 
number of minute tubules (tubuli renales), each of which has an exceedingly complicated 
course. The wall of a uriniferous tubule consists throughout of a basement membrane 
and an epithelial lining, but the diameter of the tubule and the character of the epithelium 
vary much in the different parts of each tube. Each tubule begins in a thin-walled 
spherical dilatation or capsule (capsula glomeruli), in which a complicated loop of capillary 
blood-vessels is contained. The tuft of capillaries is covered by a reflection of the delicate 
wall of the capsule, and is, as it were, invaginated into the capsule (Fig. 733). The 
oe: with their enclosed capillaries are often called Malpighian corpuscles (corpuscula 
renis), and are all placed in the labyrinth portion of the kidney cortex. The tubule 
ie from the capsule—first convoluted tubule—is much convoluted, and lies within 
the labyrinth. Passing from the labyrinth, the tubule enters a medullary ray, in which 
its course becomes less ‘complic: ited, and here it receives the name of spiral ‘tubule. From 
the medullary ray the tubule enters the intermediate zone of the pyramid, and, diminishing 
in diameter, it pursues a straight course towards the apex of the pyramid, forming the 
so-called descending limb of Henle’s loop. Within the apical portion of the pyramid the 
tubule suddenly bends upon itself, forming the loop of Henle, and reversing its direction, 
it passes back again through the intermediate zone into the medull: wy ray as the ascend- 
ing limb of Henle’s loop. This ascending limb exhibits a slight spiral twisting. Leaving 
the medullary ray, the tubule once more enters the labyrinth, where its outline becomes 
so uneven that the name irregular tubule is applied to it. While still within the laby- 
rinth, its contour having acquired a more uniform appearance, the tubule receives the 
name of second convoluted tubule ; this latter finally ends in a short junctional tubule, 
which passes back into a medullary ray and joins a collecting tube. Each collecting 
tube receives numerous kidney tubules, and pursues a straight course through a medullary 
ray and pyramid. Finally, several collecting tubes, uniting together, open as an excretory 
tube, by one of the foramina papillaria, on the surface of a renal papilla, into a calyx of 
the ureter (Fig. 733). 
