THE MALPIGHIAN BODIES OF THE KIDNEY. 
65 
they almost immediately terminate. This is the plexus surrounding' the uriniferous 
tubes. It extends from the surface to the central plane of the lobe, and there ends 
in the branches of the emulgent vein. 
Thus the efferent vessels of the Malpighian bodies are radicles of the portal vein, 
and, through the portal vein, empty themselves, as in the higher tribes, into the plexus 
surrounding the uriniferous tubes. The only real difference between this form of 
kidney and that of Mammalia, is, that there is here a vessel bringing blood that has 
already passed through the capillaries of distant parts, to be added to that coming 
from the Malpighian bodies, and to circulate, with it, through the plexus surrounding 
the tubes. The efferent vessels of the Malpighian bodies run up to the surface in 
order to throw their blood through the whole extent of the capillary plexus ; which 
they would fail to do, if they entered it in any other part. 
I have described the renal artery as being spent upon the Malpighian bodies ; but 
in the hilus of the lobe it gives off, as in the higher animals, a few slender twigs to 
the coats of the excretory ducts and of the larger vessels. The capillaries of these 
twigs are easily seen, and, in all probability, discharge themselves into the branches 
of the portal vein. 
The circulation through this form of kidney, may be aptly compared with that 
through the liver, as described by Mr. Kiernan in his invaluable paper on that gland. 
The plexus surrounding the tubes corresponds with the portal-hepatic plexus, which, 
in the lobules of the liver, invests the terminal portions of the bile-ducts. Both these 
plexuses are supplied with blood by a portal vein, derived chiefly from the capillaries 
of distant organs, but in part from those of the artery of the respective organs them- 
selves. The only difference seems to be, that, while, in the liver, the branches of the 
artery are entirely given to the larger blood-vessels, ducts, &c., in the kidney, a few 
only are so distributed, the greater number going through the Malpighian bodies, to 
perform an important and peculiar function. In both glands, however, all the blood 
of the artery eventually joins that of the portal vein. The emulgent vein of the kid- 
ney answers to the hepatic vein of the liver. 
The comparison between the hepatic and renal portal circulation may be thus 
drawn in more general terms. The portal system of the liver has a double source, 
one extraneous, the other in the organ itself: so, the portal system of the kidney, in 
the lower tribes, has a two-fold origin, one extraneous, the other in the organ itself. 
In both cases the extraneous source is the principal one, and the artery furnishing the 
internal source is very small. But in the kidney of the higher tribes, the portal system 
has only an internal source, and the artery supplying it is proportionally large. 
The above account appears to me to comprise whatever is most important in the 
anatomy of the blood-vessels and ducts of the kidney. My object in it has been to 
convey an idea of the physiological anatomy of the gland, and I have therefore omit- 
ted to mention (except where it suited my purpose) those rougher characters of the 
kidney in the various classes, that result from varieties in the mode of aggregation of 
MDCCCXLII. 
K 
