216 MR. F. E. BEDUARD ON THE [Feb. 19^ 



a pi'iori grounds, if — that is to say — we are permitted to use the 

 analogy of the development of the postcaval. It is perfectly cleai- 

 from developmental facts that in the Marsupials generally that 

 vein has a different origin postei-iorly from that which it has. 

 in the Rabbit, while McClure appears to have shown that in 

 different individuals of Didelphys marsupialis the extreme end of 

 that vein originates differently. In man, according to the facts 

 collected by Hochstetter, the postcaval has as a variation a 

 different mode of origin from that which is normal. 



In the young pouch-living individual of Macrojius derhianus de- 

 scribed above *, it was pointed out that there were two azygos veins 

 in both foetus and parent. There was no trace in either that I noted 

 of any othei' vein. It seems to me to be possible that in that and 

 other Mai'supials there are not any azygos veins at all, but the 

 persistent cardinals take their place. That this is not the case, 

 however, in Didelphys appears to be shown by McClure's investi- 

 gations t. Again, the relations of the azygos in Cervus sika 

 described above J lead one to the inference that the anterior 

 branch of the azygos running for some distance to the outside of 

 the azygos is a remnant of the postcardinal of that side, since the 

 junction of the two veins near to their entrance into the jugular 

 recalls exactl}' the conditions which have been described above in 

 the young Myopotamus. These remarks, however, cannot be 

 considered at present as more than suggested possibilities. It 

 seems to me to be equally likely that in those cases where a well- 

 develojjed right azygos or left is accompanied by a less developed 

 vein on the opposite side of the body which I have called azygos 

 in the preceding pages, the latter is really a persistent post- 

 cardinal. 



In addition to these there are cases where on one side of the 

 body at any rate both azygos and postcardinal appear to peivsist. 

 Those instances present as a permanent condition the state of 

 affairs which occurs temporarily in Myojyotamus coypii. In one of 

 two Gcelogenys p>aca described above, there is, as I regai-d it, a 

 well-developed persistent postcardinal on the right side and traces 

 of the same on the left, in addition to a well-developed azygos 

 on the right and a good but not so well-developed azygos on 

 the left. In Capromys j)ilorides there are also considerable 

 remains of the right postcardinal as well as of the right azygos. 

 In Hystrix cristata (see text-fig. 72, p. 211) we see precisely the 

 same thing on the right side ; in this species in both examples 

 dissected. Bolicliotis p)atachon%ca has also, if my views are correct, 

 both a right azygos and a short right postcardinal. Noi- is this 

 retention of a fcetal condition peculiar to Rodents, though clearly^ 

 so far as my experience goes, most abundant in them ; for it also 

 occurs on the right side of the body in Cervus sika. 



The relationshiji of the posterior end of the azygos to the 

 postcardinal of the right side requires further emphasis. As has 



* Supra, p. 202. f Loo. cit. p. 183. X Snpra, p. 192. 



