Variability of the v. cava caudalis and its tributaries in some laboratory animals. II. The laboratory rat (Rattus norvegicus v. alba).

Duplication of the v. renalis was found in 11 of the regions examined (18.3%), when it was more frequent on the right side. A v. capsularis was found in 35 regions (58.3%), usually as a single vein. There were 1-3 vv. suprarenales (but mostly two; on the right they usually joined the v. cava caudalis and on the left the v. renalis sinistra). A v. spermatica was present on the right side in every case, but on the left side in 11 cases only; in one case it was duplicated. In the rat, the v. spermatica was rather thin; if absent, it was replaced by the v. deferentialis. In nine cases (60.0%) the v. uterina cranialis dextra opened into the v. cava caudalis, while in 12 cases (80.0%) the left vein opened into the v. renalis sinistra. A v. uterina media, draining blood from the caudal third of the cornu uteri, was found in only five cases (16.7%). The v. uterina caudalis drained blood from the corpus and cervix uteri. The v. ovarica was a constant finding; it was mostly joined by the v. lumbalis--and on the left side by the v. phrenica sinistra. In males, the vv. lumbales occurred mostly as a pair of veins lying just below the vv. renales. In females, they were present on both sides. As a rule, the v. iliolumbalis occurred as a single vein on both sides. The v. cava caudalis originated at the level of the transition between the lumbar and the sacral spine, usually at the confluence of the two vv. iliacae communes, which in 14 cases (46.7%) were joined by the v. sacralis mediana. Duplication of the v. cava caudalis was found in only one case (a female). Comparison of the morphology of the v. cava caudalis and its tributaries in the rat and the guinea pig showed more slight differences between the two species.