Charles F. W. McClure 383 
third, and, on the right side, as far caudad as the second lumbar ver- 
tebra, is collected by the tributaries of this vein. The blood from the 
rest of the lumbar region is collected by the lumbar veins which open 
into the postcava. The blood from the first intercostal space is col- 
lected, on both sides, by the superficial superior intercostal vein 
(V. i. s. I, Text Fig. III), which opens into the V. costovertebralis; 
that from the second intercostal space by a vein which opens directly 
into the deep superior intercostal (g. and V.i. s. II, in Text Fig. II) 
without previously anastomosing with any of the azygos branches. 
The intercostal tributaries of the azygos anastomose with the Vy. 
column vertebrales in the caudal part of the thorax, and, in the 
cranial part, with the deep superior intercostal (V. i. s. II), which, as 
mentioned above, is one of the tributaries of the V. costovertebralis 
(Hext Hig. TI £:): 
The relation of the azygos tributaries to the first four intercostal 
spaces was found to be quite variable and this was especially the case 
on the right side. In five opossums (three males and two females) the 
most cranial tributary of the azygos, on the right side, collected blood 
from the fourth instead of from the third intercostal space, as is usu- 
ally the case, and the veins of the second and third intercostal spaces 
opened directly into the deep superior intercostal vein without anasto- 
mosing with the azygos. The blood from the first intercostal space 
was collected by the superficial superior intercostal vein. On the left 
side the arrangement of the veins was similar to that represented in 
Text Fig. IV. 
Two instances were met with in which tributaries of the azygos col- 
lected blood from all of the intercostal spaces, on both sides, with the 
exception of the first and anastomosed with the tributaries of the Vv. 
costovertebrales which le caudal to the first ribs (e.). 
In thirty per cent of the opossums examined a small right azygos 
vein was present which opened into the right precava about opposite 
the head of the second rib. In every instance the vein was a small 
and insignificant vessel and its tributaries were confined to the first 
five intercostal spaces of the right side. In the eight animals in 
which it was found it collected blood in three, from the second inter- 
costal space; in one, from the second and third intercostal spaces; in 
one from the third intercostal space; in two, from the third and fourth 
intercostal spaces, and finally, in one, from the third, fourth and fifth 
intercostal spaces. When the right azygos received tributaries from the 
third, fourth or fifth intercostal spaces, the tributaries of the left azy- 
gos which usually collect blood from these spaces were wanting. 
