62 
MR. BOWMAN ON THE STRUCTURE AND USE OF 
and form the plexus with long meshes which invests this part of the tubes. Some of 
the veins springing from this plexus form the well-known network on the nipple- 
shaped extremities of the cones, around the orifices of the tubes, and thence take, 
with the remainder, a backward course, likewise parallel to the tubes, to empty them- 
selves into venous branches that lie about the bases of the cones. These also, when 
injected, have been mistaken for tubes. 
The other venous radicles are dispersed at about equal distances throughout the 
cortex of the kidney, and each receives the blood on all sides from the plexus sur- 
rounding the convoluted tubes. When these venous radicles are congested, or injected, 
they mark out the surface of the cortical substance into lobules not very unlike those 
of the lobules of the liver. On the Horse’s kidney, especially, this may be often well 
seen. Each lobule contains many tortuous ducts with their capillaries, but the con- 
volutions of any one duct are not confined to a single lobule. These radicles unite 
in an irregularly arborescent figure, anastomose and form the several branches of the 
renal vein. Those on the surface, especially of the human kidney, have a tendency 
to converge towards a central vessel which then dips into the interior, and runs, like 
the rest, towards the hilus. Thus are formed the stellated vessels of anatomists, often 
conspicuous in diseased specimens. Between the sprawling arms of these stellee the 
convoluted tubes, with their plexus, come up to the surface (Plate IV. fig. 11), but the 
Malpighian bodies are rarely, if ever, visible quite on the surface. They are always 
covered in by convolutions of the tubes. 
The veins from the capsule and surrounding fat join the renal vein in some part of 
its course. It is probable that the capillaries of the vasa vasorum, within the sub- 
stance of the organ, pour their blood into the capillary plexus surrounding the tubes, 
as those of the hepatic artery do into the portal-hepatic plexus of the lobules of the 
liver. 
Thus there are in the kidney two perfectly distinct systems of capillary vessels, 
through both of which the blood passes in its course from the arteries into the veins : 
the 1st, that inserted into the dilated extremities of the uriniferous tubes, and in im- 
mediate connection with the arteries ; the 2nd, that enveloping the convolutions of 
the tubes, and communicating directly with the veins. The efferent vessels of the 
Malpighian bodies, that carry the blood between these two systems, may collectively 
be termed the portal system of the kidney. To these distinct capillary systems, I am 
inclined to attribute distinct parts of the function of the organ ; and their importance 
seems to warrant a few words, in further explanation of their anatomical differences. 
The former, which may be styled the Malpighian capillary system, is made up of 
as many parts as there are Malpighian bodies. These parts are entirely isolated from 
one another ; and, as there is no inosculation between the arterial branches supplying 
them, the blood enters each in a direct stream from the main trunk. This capillary 
system is also highly remarkable, indeed stands alone among similar structures, 
in being hare. The secreting tubes of the kidney, like those of all other glands, are. 
