1889. ] CARDINAL VEIN IN THE FROG, 147 
Howes (except that there was no anastomosis with the renal portal), 
could be seen opening into what appeared to be the inter-renal portion 
of the posteaval (7.cd). Upon further examination it was found that 
there was no posteaval trunk extending from this inter-renal vessel 
to the heart, and the apparent azygos was thus the completely per- 
sistent left posterior cardinal. The renal portion of the right cardinal 
must therefore have fused with its fellow in the usual manner to form 
the large median vessel, which ordinarily gives rise to the posterior 
part of the postcaval, while its anterior part disappeared, although 
the hepatic portion of the postcaval remained undeveloped. The left 
eardinal, united with the renal portion of the right, had thus to 
serve as the channel for all the blood from the posterior extremities, 
&c., except that which entered the liver by the anterior abdominal 
vein, which had the usual relations. The hepatic veins (/.v) 
opened directly into the sinus venosus. The spermatic vessels 
(sp) were very asymmetrical, as were the ovarian vessels in Howes’s 
specimen. 
Hochstetter states that the hepatic portion of the postcaval 
remains undeveloped exceptionally in the Salamander, in which case 
either one or the other cardinal becomes correspondingly enlarged. 
It is known, too, that in Man the lower portion of the left cardinal 
is occasionally present, and that the postcaval sometimes remains 
undeveloped, the blood being returned to the heart by a persistent 
posterior cardinal, in which case the hepatic veins open independently 
into the right auricle’. 
It is extremely interesting to find these exceptions to the rule 
that all air-breathing animals (Amphibia and Amniota) possess a 
postcaval, and they seem to completely support Hochstetter’s views 
as to the mode of formation of the postcaval. 
The observations described and referred to above have helped me 
considerably in the determination of the homology of the two veins in 
Protopterus which have usually been described as ven cave pos- 
teriores. At the time when my paper “ Zur Anatomie und Physiologie 
von Protopterus annectens”’”, giving a preliminary account of the 
work on which I am still engaged, was published, 1 had made only a 
very cursory examination of the veins, and this had led me to the 
conclusion that “das was man bisher bei Dipnoérn als Vene cave 
posteriores bezeichnet hat, sind sicherlich keine solchen, sondern 
entsprechen den (allerdings einigermassen modificirten) Vene 
cardinales posteriores.”’ 
Owing to the extreme difficulty in following out the venous system 
in preserved specimens of Protopterus, I have not even yet completely 
satisfied myself as to the exact relations of all the vessels. But 
since the above-mentioned paper appeared, I have succeeded in 
elucidating some important points which were then by no means 
clear. 
Dr. Hochstetter has recently been good enough to make several 
' Quain’s Anatomy, 9th ed. vol, i. pp. 514, 518. 
* Berichte der naturforschenden Gesellschaft zu Freiburg i. B., [V. Band, 3 
Heft. See also ‘ Nature,’ vol. xxxix. 1888, p. 9. 
