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EXPLANATION OF FIGURES ON PLATE I. 
Fie. 28. Arteries and veins of an adult female Opossum (Didelphys marsu- 
pialis, L. or, as more commonly called, D. virginiana, Kerr, L.). Ventral view. 
Heart reflected to the right and liver, for the most part, cut away. The post- 
cava is formed as in Type II, in which the internal iliac veins unite with 
the external iliacs dorsal to the common iliac arteries. In addition to the 
Type of postcava mentioned above the following features should be noticed: 
The peculiar course pursued by the V. cordis magna; the position occupied by 
the azygos vein with respect to the segmental arteries; the absence of the 
anterior and posterior mesenteric arteries; the anastomosis between the renal 
and spermatic veins which lies on the medial side of the ureter, and the two 
pairs of internal spermatic arteries. 
EXPLANATION OF FIGURES 29 to 61 ON PLATES II-V. 
PATE Lil 
Figures 29-36. 
Fics. 29 (section 164) and 30 (section 171). Transverse sections of a 
6 mm. embryo of Dasyurus, Series I. 
Fics. 31 (section 187), 32 (section 208), 33 (section 211), 34 (section 225), 
35 (section 226) and 36 (section 238). Transverse sections of an 8 mm. 
embryo of Didelphys, Series VIII. 
