64 
MR. BOWMAN ON THE STRUCTURE AND USE OF 
The capillary plexus surrounding the tubes differs, therefore, from that of other 
glands, and agrees with that of the liver, in its receiving blood that has previously 
traversed another system of capillary vessels. That other system is a peculiar one, as 
already pointed out, and cannot be likened closely to that which furnishes the portal 
vein of the liver. 
The preceding account of the existence of a true portal system in the kidney of the 
higher tribes of Vertebrata was already written, when an opportunity presented itself 
of inspecting the distribution of the vessels in one of those lower animals, in which, 
besides the renal artery, the kidney is furnished with a portal vein, derived from the 
hinder part of the body. The presence of such a vein, though denied by Meckel, 
was well established by Nicolai, whose statements have been confirmed by others ; 
but I am not aware that any anatomist has explained its remarkable distribution, and 
its connection with the other vessels *. I shall therefore introduce a summary ac- 
count of my examination of the kidney of the Boa Constrictor (the animal in ques- 
tion), which may be regarded as a model of this variety ; and I think it will be found 
not only to show the correctness of the analogy I have drawn between the efferent 
vessels of the Malpighian bodies and a portal system, but to place in a clearer light 
the other striking resemblances between the circulation of the liver and kidney. 
The kidney of the Boa, being composed of isolated lobes, of a compressed reniform 
shape, displays all the points of its structure in peculiar simplicity and beauty. At 
what may be termed the hilus of each lobe, the branches of the vena porta and duct 
separate from those of the renal artery and emulgent vein ; the two former spreading 
side by side, in a fan-like form, over the opposite surfaces of the lobe, while the two 
latter enter its substance, and radiate together in a plane midway between these sur- 
faces. The lobe is made up of the ramifications of these four sets of vessels, in the 
following mode. Each duct , as it runs over the surface, sends down a series of 
branches which penetrate in a pretty direct manner towards the central plane. Arrived 
there, they curl back, and take a more or less retrograde course towards the surface, 
and finally, becoming more convoluted, terminate in the Malpighian bodies, which 
are all situated in a layer at some distance within the lobe, parallel to the central 
plane, and nearer to it than to the surface. The ducts never anastomose. The artery 
subdivides into extremely minute twigs, no larger than capillaries, which diverge on 
either hand, and enter the Malpighian bodies. The efferent, vessels are of the same 
size as the afferent, and on emerging, take a direct course to the surface of the lobe, 
and join the branches of the vena porta there spread out. The branches of the portal 
vein on the surface, send inwards a very numerous series of twigs of nearly uniform 
capacity, and only a little larger than the vessels of the capillary plexus, in which 
* Huschke, who seems to have entered into the greatest detail on this subject, states that he was unable to 
ascertain in the Serpent’s kidney, whether the twigs of the artery were distributed to the Malpighian bodies or 
not. In the Frog, however, he describes the Malpighian bodies as appended to the terminal twigs of the artery. 
Isis, 1828, p. 566-7. 
