1889.] CARDINAL VEIN IN THE FROG. 147 



Howes (except that there was no anastomosis witli the renal portal), 

 could be seen opening into what appeared to be the inter-renal portion 

 of the postcaval (r.cd). Upon further examination it was found that 

 there was no postcaval trunk extending from this inter-renal vessel 

 to the heart, and the apparent azvgos 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. Tlie left 

 cardinal, 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 (h.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 tiie 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 venae cavge pos- 

 teriores. At the time when my paper " Zur Anatomic und Physiologie 

 von Protopte7-us unnectens " ^, giving a preliminary account of the 

 work on which I am still engaged, was pubHshed, 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 Dipnotrn als Veyice cavce 

 posleriores bezeichnet hat, sind sicherlich keiue solchen, sondern 

 entsprechen den (allerdings einigermassen modificirten) Fence 

 cardinales postei-iores." 



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 



1 Quain's Anatomy, 9tli ed. vol, i. pp. 514, 518. 



^ Berichte der naturforschenden Gesellschaft zu Freiburg i. B., IV. Band, 3 

 Heft. See also ' Nature,' vol. xsxix. 1888, p. 9. 



