BLOOD-VASCULAR SYSTEM, ETC., OF AMIURUS CATUS. 429 
artery The two posterior trunk vertebre have short and _ broad ‘ 
hzemal arches united by a transverse piece. The caudal vein turns 
downwards over the posterior face of the second (sometimes the first) 
and enters the kidney, which extends back over these arches. It 
then passes downwards and forwards through the substance of the 
kidney and near the ventral surface gives off two branches, first a right 
and then a left vena renalis advehens, which, passing forwards and 
outwards, distribute their blood to the kidney. 
The caudal vein, leaving the kidney, is attached to the mesentery 
which unites the genital glands and becomes the portal vein, running 
straight forward beneath the air-bladder to the liver. This arrange- 
ment has not been described for any of the T'eleostei, as far as I am 
aware, and if Nicolai and Hyrtl are correct does not occur in other 
Siluroids. According to these observers the entire vein distributes 
itself to the kidney as the vena renalis advehens. The former 
arrangement was constant in all specimens of Amiwrus catus ex- 
amined by me. 
The posterior cardinals (ven vertebrales posteriores of Stannius) 
arise in the kidney and run forward on each side of the vertebral 
column. Asin other Teleosts the left vein is very small in com- 
parison with the right, which, by a median stem, drains almost the 
entire kidney, and issuing upon its anterior concave surface passes 
upward and to the right, to the side of the vertebral column, where it 
forms a large sinus-like vessel. ‘The left cardinal receives only a few 
branches from the horn of the kidney upon that side. Upon reach- 
ing the fourth vertebra they narrow to pass through a triangular 
foramen formed by the body of the vertebra at the side, the trans- 
verse process above and an oblique bony ledge below. Having passed 
through they turn downwards through the head-kidney and join the 
anterior cardinals. 
The veins which drain into the vena caudalis, do not require any 
special description, but when this vein leaves its position beneath the 
aorta upon entering the body, it causes its branches to vary also from 
the branches of the latter. 
The portal vein receives the genital veins in its passage between 
these organs. It then passes above and in contact with the spleen 
receiving the splenic veins. This point also forms a sort of nucleus 
for the entry of a number of veins from the left mesenteric fold. 
Those on the right unite into a mesenteric vein which in some speci- 
