Charles F. W. McClure 381 
Vy. columne vertebrales (Vv. c. ve.), and, on its lateral side, with the 
descending cervical vein (V. ¢. d.). 
4. The deep V. intercostalis suprema (V. i. s. II) is a comparatively 
short vessel which runs, on each side, parallel to the vertebral column 
and extends between the second and sixth to seventh ribs dorsal to 
their necks. This vein opens into the vein, previously mentioned, 
that lies caudal to the first rib (e.) and collects blood from the 
second to sixth intercostal spaces. It anastomoses in this region 
with the intercostal branches of the azygos (f.) and, opposite the head 
of each rib, by means of a large anastomosis with the Vv. columne 
vertebrales. It also receives two important tributaries: (1) The vein 
of the second intercostal space (g.), which usually opens into it without 
previously anastomosing with the azygos branches, and (2) a vein (h.) 
which collects blood from the deep muscles on the back of the neck and 
joins the deep superior intercostal vein (V. i. s. Il) about opposite the 
third intercostal space.” 
In comparing the veins of Didelphys, as represented by the V. costo- 
vertebralis and its tributaries, with the vertebral system of veins in 
the sauropsida, especially birds, one cannot help being impressed by 
the similarity that exists between the two. In Didelphys the verte- 
bral and deep superior intercostal veins occupy the same 
relative positions with respect to the vertebral column and 
connect with the jugular and subclavian veins to form the 
precava, as do the anterior and posterior vertebral veins in 
birds. In birds, there being no azygos vein, all of the intercostal 
veins open directly into a posterior vertebral vein. In Didelphys, also, 
some of the veins of the cranial intercostal spaces may open directly 
into the deep superior intercostal without previously anastomosing 
with any of the azygos branches (see under Azygos Veins). 
THE VENA AZYGOS AND ITS TRIBUTARIES. (See Teat Figs. III and IV.) 
There is, as a rule, but one azygos vein in Didelphys and this is 
situated on the left side. The azygos vein increases slightly in size 
from behind forward. Its caudal end invariably joins the postcava 
about opposite the second lumbar vertebra, while its cranial end, after 
curving round the left side of the aorta, joins the left precava about 
Wn Didelphys a branch of an intercostal artery accompanies this vein. Cunningham 
(82) has described the course of this artery in Thylacinus and Dasywrus but did not 
mention the vein. 
11 The azygos system was dissected in twenty-six opossums. 
