24 Macueay Memoria Vouume. 
F. Derivatives of the posterior cardinal system. 
Under this head may be considered two important vessels, one on the right and 
one on the left side of the body. There can be, I think, little doubt but that one of 
these is the representative of the left posterior cardinal vein of a typical fish ; whilst 
the other may be rightly regarded, judging from its relationships, as intimately 
associated with a similar right posterior cardinal vein. The significance of this will 
be discussed later. 
In this system we have again an instance of the asymmetrical development of 
the blood vessels which has been already noticed in connection with the pulmonary 
arteries and the anterior abdominal system. 
(1) Posterior cardinal of the left side (figs. 10, 15, and 16). 
It was noted when dealing with the caudal vein that this, after passing 
downwards from the hzmal arch, divides into two branches, between the kidneys, of 
which branches the right is considerably larger than the left. The left branch into 
which open two revehent branches from the kidney of its side passes onwards to the 
left flat band-like testis (or to the ovary). Accompanied by the artery, it runs along 
the whole length of the latter on the inner side close to where the mesentery attaches 
it to the wall of the intestine (fig. 10). It can be easily injected in either direction. 
Traced forwards the artery and vein are found to run onwards to the very 
anterior end of the body cavity above the level of the liver. From the testis, or 
ovary, as the case may be, the vein receives numerous branches during its course. 
Just beyond the anterior end of the body cavity the artery which lies to the outer 
side of the vein crosses dorsad of the latter and runs forwards to join the brachial 
artery of its own side close to the dorsal aorta, as previously described. 
The vein runs on forwards and at the same time slightly downwards giving 
off a curious anastomotic branch to the brachial artery (figs. 2 and 15, x.), beneath 
which it passes until it reaches the point at which the superior jugular and the 
subscapular veins join together to open into the Ductus Cuvieri (fig. 15). It then 
falls into the vessel formed by the union of these two. 
There can, I think, from its relationship—viz., its origin from the caudal vein, 
connection with the kidney and final opening into the Ductus Cuvieri—be no doubt 
but that we are here dealing with a posterior cardinal vein, though perhaps slightly 
modified, such as is characteristic of the piscine type. 
