A CONTRIBUTION TO THE ANATOMY AND DEVELOPMENT 
OF THE VENOUS SYSTEM OF DIDELPHYS 
MARSUPIALIS (L).’ 
Part [I], DEVELOPMENT. : 
BY 
CHARLES F. W. McCLURE. 
Professor of Comparative Anatomy, Princeton University. 
WitH 5 DouBLE PLATES AND 27 TEXT FIGURES. 
A number of publications have appeared, especially the monographs 
of Selenka, 86-7 and g1, and Semon, 94, in which have been described 
the arrangement of the blood vessels in the extra-embryonic vascular 
area of marsupials. So far as known to the writer, however, the only 
actual contributions that have been made to the development of the 
intra-embryonic venous system of this group of mammals are one by 
Broom, 98, and a preliminary notice by the writer, 02. 
The publication of the present paper (Part IL) has been unavoidably 
delayed, owing to the writer’s inability to obtain embryos sufficiently 
young to show the earliest stages in the development of the postcaval 
vein. These early stages have, unfortunately, not yet been obtained, and 
were it not for the circumstance that so little has been published upon 
the development of the veins of marsupials, an apology would be due for 
presenting what must necessarily be an incomplete account. 
In writing this paper the writer has fully borne in mind the danger 
involved of drawing conclusions from an incomplete series, and, in the 
case of Didelphys, the danger is especially great on account of the vari- 
able character of its venous system. A complete account of the develop- 
ment of the veins of Didelphys, especially of the variations of the post- 
cava, necessitates not only a complete series of embryos and pouch 
young, but a number of examples from each stage as well. Such an 
1The publication of this paper in two parts, one dealing with the Anatomy 
(Part I) and the other, or present paper (Part II), with the Development of 
the venous system, was unavoidable and it is, therefore, to be hoped that the 
frequent references made in the following pages to Part I will not prove too 
great a source of confusion or inconvenience to the reader. 
Part I of this paper was published in The American Journal of Anatomy, 
Vol. II, No. 3, 1903. 
AMERICAN JOURNAL OF ANATOMY.—VOL. V. 
