714 
PROFESSOR T. J. PARKER ON THE 
The cardinal veins. 
Abdominal cava, vena cava, Monro (16). 
Vertebralvene, Muller (17). 
Vena vertebralis posterior, Stannius (25). 
Veine abdominale, Milne Edwards (14), 
Vena cardincdis, Owen (19). 
Cardinal vein, Huxley (10). 
The cardinal veins (Plate 34, fig. 1 ; Plate 35, fig. 10 ; Plate 37, figs. 22, 23, and 24, 
Card. V.) lie immediately ventrad of the vertebral column. They are unsymmetrically 
developed, the right trunk (R. Card. V.) only being complete, and the left (L. Card. V.) 
uniting with it a short distance caudad of the anterior end of the kidneys. Posterior 
to the point of union with its fellow the right cardinal is situated in the middle line 
imbedded in the fused kidneys (figs. 23 and 24), and therefore not visible in the 
ordinary course of dissection without partly removing the latter; traced backwards 
it is found to undergo a gradual diminution in calibre, and to arise at the posterior end 
of the kidneys by the confluence of the efferent veins from that part of the renal 
tissues. 
It has already been shown (supra, p. 703) that the caudal vein, contrary to the 
statements usually made, divides into two renal portal veins which pass forwards, 
gradually diminishing in calibre. It is now shown that the cardinal vein, so far 
from being continuous with the caudal, commences as a very small vessel in the 
posterior region of the kidneys, and extends forwards, gradually increasing in 
calibre. These facts are clear enough from ordinary dissection ; if an injected 
specimen be hardened in alcohol, the cardinal vein slit open longitudinally and the 
contained injection-mass removed, the non-extension of the vein caudad of the 
kidneys is perfectly evident. But the matter becomes clearer still by the examina¬ 
tion of a series of sections, as shown in Plate 37, figs. 22-24. In fig. 22, taken 
through the middle of the first dorsal fin and a short distance cephalad of the union 
of the left cardinal with the right, the renal portal veins are very small; in fig. 23, 
taken 4 cms. cephalad of the pubis, the right cardinal is seen to have taken up a 
median position and the renal portals have increased in size ; in fig. 24, through 
the symphysis pubis, the renal portals have still further increased in calibre and 
are now distinctly larger than the right cardinal, which, in the next section, had 
disappeared. 
It will be for future investigations to determine the age at which the formation 
of the renal portal system takes place, all that can be said at present being that 
it occurs during comparatively late embryonic life. In the embryo of Scymnus, 
already referred to (“ Stage 0,” Balfour), the caudal vein is directly continued 
into the cardinals as in Cyclostom.es (Plate 37, figs. 31 and 32) ; on the other 
hand, in a ripe foetus of Mustelus I have ascertained, from a complete series of 
