Charles F. W. McClure 401 
(paired portion) extend caudad, at first lying ventral to and then on 
either side of the aorta, and caudal to the A. mesenterica posterior 
(A.m.p.) anastomose with each other ventral to the aorta. The two 
internal iliac veins (V.i.i.) which, as Hochstetter says, must be regarded 
as continuations of the postcaval veins now open into this anastomosis 
ventral to the common iliac arteries. 
In the older embryo (No. 45, Text Fig. XI), the unpaired portion of 
the postcava possesses the same relations as in embryo No. 44. In the 
paired portion, however, important changes have taken place. Here ‘the 
anastomosis between the two postcaval veins caudal to the posterior 
mesenteric artery (A.m.p.) no longer exists, and the postcava is now 
formed as in Type III, B, of Didelphys (Fig. 18, Plate IV), in which 
the internal iliac veins (V.i.i.) anastomose ventral to the A. sacralis 
media (A. s. m.) and unite with the external iliacs (V. i. e.) to form 
the posteava by means of three vessels two of which lie dorsal and one 
ventral to the iliac arteries. The transformation of this stage into the 
adult condition takes place through the atrophy of the vessel 
which lies ventral to the iliac arteries. The result is that a 
posteava is formed in Hchidna similar to that of Type II in Didel- 
phys, in which the internal iliac veins join the external iliacs 
dorsal to the common iliac arteries, which is also the Type in 
Didelphys in which the posteava was found to be most fre- 
quently bifurcated. 
THE V. PUDENDOVESICALIS. 
The V. pudendovesicalis (V. p. v. in Figs. 1, 8 and 23, Plates I, II and 
V) of Didelphys, which returns blood from the bladder and external gen- 
ital organs, apparently has no regular method of opening into the iliac 
veins. The remarkable yariations presented by these veins will not be 
further considered here, however, as they have already been fully described 
by the writer in a former paper (McClure, 00, p. 457) to which the reader 
is referred. 
LITERATURE. 
1895. Brpparp, F. E.—On the Visceral Anatomy and Brain of Dendrolagus 
bennitte. Proc. of Zool. Soe. of London for 1895. 
1902. BrppARD, F. 4.—Mammailia. 
1882. CUNNINGHAM, D. J.—Challenger Reports, Zoology, Vol. V. 
1898. DrEvEez, G—Une point d’Anatomie du ventricule droit des Didelphys. 
Bull. Mus. Hist. Nat., Paris, Année, 1898. 
1881. Forbes, W. A.—On some points in the Anatomy of the Koala 
(Phascolarctos cinereus). Proe. of Zool. Soe. of London for 1881. 
