PARKER AND TOZIER: POSTCARDINAL VEINS IN SWINE. 137 
by the azygos vein was transferred by transverse connecting vessels to 
the hemiazygos, by which it was carried to the heart. In the specimen 
from which the reconstruction shown in Figure 3 was made, three such 
transverse connections were found. In a specimen fifty-five millimeters 
long, studied by injection, five such vessels occurred, and these were so 
placed that their ends were opposite the mouths of the newly forming 
intercostal veins. 
The most striking peculiarity of the stage illustrated by Figure 3 is its 
lack of symmetry. In the earlier conditions described these veins have 
been bilaterally symmetrical ; but with the loss of connection between 
the azygos and the right Cuvierian duct this symmetry disappears, and 
a connection with the heart is retained only through the left side. In 
this respect the pig and probably all ruminants differ from other mam- 
mals, in which as a rule the azygos, not the hemiazygos, recains its 
original connection with the heart. 
The further changes that the azygos and hemiazygos undergo may 
be seen in pigs ranging in length from seven to twenty centimeters. 
The chief features of these changes consist in the further reduction of 
the azygos, together with the retention of the transverse connecting 
vessels, by which the right intercostals are brought to connect directly 
with the hemiazygos. Depending upon the way in which the azygos is 
reduced, three types can be distinguished. These are illustrated in 
Figure 4. 
In the first type (Fig. 4, A) the hemiazygos reaches from the heart 
posteriorly to the eleventh intercostal space, receiving in its course the 
intercostal veins on the right from the sixth to the eleventh, and on the 
left from the fifth to the eleventh. Posterior to the eleventh intercostals 
two longitndinal veins appear, which are of about equal size, and extend 
posteriorly two segments farther, receiving the twelfth and thirteenth 
intercostals. Of these the left one (vn. hm’az.) obviously represents the 
posterior continuation of the hemiazygos, the right one (vn. az.) the last 
remnant of the azygos, which in the region of the eleventh intercostal 
still retains its transverse connection with the hemiazygos. 
In the second type (Fig. 4, B) the hemiazygos (vn. hm’az.) excends 
as the predominant vessel from the heart to the fourteenth intercostal 
space. The azygos is entirely suppressed, except for a small part run- 
ning from the twelfth to the thirteeth intercostal and possessing at its 
two ends transverse connections with the hemiazygos. 
In the third and last type (Fig. 4, C) the hemiazygos is a well devel- 
oped trunk from the heart to the ninth intercostal, beyond which the 
