452 



As in the case with the variations in regard to the formation 

 of the V. cava posterior, there appears to be no relation between 

 sex or age and the presence of a bifurcation or of indications of a 

 bifurcation of the V. cava posterior. 



The above table shows that over 50 per cent of the opossums 

 examined either possess a bifurcated V. cava posterior or some 

 indication of the same. In no instance, however, did the bifurcation 

 reach higher than the level of one or both of the Vv. spermaticae. 

 See Figs. 3 and 4. Six examples of this type of bifurcation were 

 met with distributed among three males and three females. 



In four instances, among two males and two females, the 

 V. cava posterior presented what might be called an indication of 

 a bifurcation. In these cases, however, the bifurcation did not reach 

 as high as the level of the Vv. spermaticae. See Figs. 8, 12 and 

 14. These cases although they may not possess the same signi- 

 ficance, closely resemble those recently described by the writer for 

 the cat, as instances of unusually long Vv. iliacae communes ^). 



In four instances, among two males and two females, foramina 

 were met with in the V, cava posterior at the level of the 

 Vv. spermaticae. See Figs. 14, 15 and 16. It is interesting to note 

 in this connection that when a foramen was found to be present, 

 in every instance the Aa. spermaticae-) passed through it. It may 



1) McClure, On the Frequency of Abnormalities in connection 

 with the Postcaval vein and its Tributaries in the Domestic Cat (Felis 

 domestica). The American Naturalist, Vol. 34, 1900, No. 399. 



2) The mode of origin of the Aa. spermaticae from the Aorta was 

 found to be quite variable. In some instances thej^ arose by a common 

 trunk (Fig. 15); while in others, they arose as single vessels (Fig. 3); 

 and in one case both arteries were given off from the same side of the 

 Aorta (Fig. 7). 



In a recently dissected adult female opossum, killed during the 

 breeding season, the writer observed two pairs of sub -equally 



