134 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
digesting fluid, thus leaving the courses of the vessels indicated by the 
celloidin, From embryos of intermediate size both reconstructions and 
injections were made, and the results obtained by the two methods 
compared. 
Observations on Swine. 
In an embryonic pig, whose greatest length as measured in a straight 
line from the crown of its head to the root of its tail, was between 
six and seven millimeters, a reconstruction of the primary veins of 
the trunk, when viewed ventrally, ap- 
peared as in Figure 1. From the ante- 
rior end of the embryo, two veins, the 
right and left precardinals (prerd. d. 
and pr’erd. s.), pass posteriorly to the 
PAGADA, region of the heart, where each is 
met by a’ corresponding postcardinal 
(p’erd. d. and p’erd. s.). The pre- 
and postcardinals of either side unite 
PRICAD.D.* = =) 
oT Cuv. D.--- 
P'CRD.D ~~ 
to form transverse trunks, the right 
and left Cuvierian ducts (dt. Cuv. d. 
and dt. Ouv. s.). The ducts thus formed 
unite with each other, giving rise to the 
venous sinus (sn. vn.), through whose 
posterior wall three large veins enter 
from the liver, and in whose anterior 
wall the passage to the heart is seen. 
decor i Of these veins the postcardinals 
(perd. d., and perd. s.) claim our 
special attention. At this stage they are symmetrical. Each begins 
posteriorly by a union of several small veins at the base of the hind leg 
of its own side of the body, and in a region dorsal and lateral to the 
mesonephros (ms’nph.) of the same side. From this region the vein 
extends anteriorly over the dorsal surface of the mesonephros, penetrating 
more or less completely the anterior end of that organ, and emerging 
from it to pass directly, as a well defined blood-vessel, to the Cuvierian 
Fig. 1. Reconstruction on a frontal plane of the principal veins and the 
mesonephroi of an embryonic pig between six and seven millimeters long. Ventral 
view. X 12. dt. Cuv. d., right Cuvierian duct; dt. Cuv. s., left Cuvierian duct; 
ms’nph., mesonephros; p’erd. d., right postcardinal; p’erd. s., left postcardinal ; 
pr’crd. d., right precardinal ; pr’erd. s., left precardinal; sn. vn., venous sinus. 
