380 Venous System of Didelphys Marsupialis 
The V. costovertebralis (V. cv.), previously mentioned as one of 
the tributaries of the precava, is most intimately connected with this 
deep-lving svstem of veins and may, therefore, be considered at this 
point. 
Fig. Ill. Diagram of the veins of the 
vertebral canal and the deep-lying veins 
of the cervical and thoracic regions of 
Didelphys marsupialis. Ventral view. 
d.and e. tributaries of the V. costoverte- 
bralis which lie cranial and caudal, re- 
spectively, to the first rib; cl., clavicle; f., 
anastomosis between the azygos and inter- 
costal veins and the veins of the vertebral 
canal; g., vein of the second intercostal 
space; h., tributary of the deep superior 
intercostal vein; pre., precava; R.I-R.VL., 
the first six ribs; V.a., intercostal branches 
of azygos vein; V.c.d., V. cervicalis descen- 
dens; V.cy., V. costovertebralis; V.i.s.I., 
superficial V. intercostalis suprema; 
V.i.s.II., deep V. intercostalis suprema; 
V.j.e.,V. jugularis externa; V.j.i..V. jugu- 
larisinterna; V.v.,V. vertebralis; Vv.c.ve., 
Vy. column vertebrales. 
The tributaries of the V. costoverte- 
bralis (V. cv.) are, on each side, as 
follows: (1) A small superficial V. 
intercostalis suprema(V.i.s. 1); (2) 
two large veins, one of which lies just 
cranial (d.) and the other caudal (e.) 
to the first rib (R. 1); (3)ethemye 
vertebralis (V. v.), and (4) a deep- 
lying V. intercostalis suprema (V. 1. s. 
iS) 
1. The superficial V. intercostalis 
suprema (V. i. s. 1) commonly opens 
into the V. costovertebralis, but may, 
instead, open into the precava. It lies 
superficially, collects blood from the 
first intercostal space and usually 
anastomoses directly with the second 
intercostal vein (g., right side). 
2. The largest tributaries of the V. 
costovertebralis consist of two large 
veins, one of which lies just cranial 
(d.) and the other caudal (e.) to the 
first rib. Both of these veins connect 
directly with the Vv. column verte- 
brales (Vv. c. ve.). The vein cranial 
to the rib is sometimes the larger of 
the two, though, as a rule, they are 
subequal in size. These two vessels 
occupy a position in the cervical and 
thoracic regions directly in the line of 
the segmental vessels and appear to 
correspond to the last cervical and first intercostal veins, respectively. 
3. The V. vertebralis (V. v.) lies in the vertebraterial canal with the 
vertebral artery and opens into the large tributary of the V. costo- 
vertebralis which lies just cranial to the first rib (d.). It anastomoses, 
by means of segmentally arranged vessels, on its medial side, with the 
. 
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