The uterine vascular system of the golden hamster and its changes during the oestrous cycle.

The vascular pattern of the hamster uterus and its changes during the oestrous cycle were studied by using the corrosion vascular casting method. The vascular system of the hamster uterus has two main division, the circumferential division and the medial arterial division. The former consists of circumferential and radial vessels and supplies the major part of the uterus. In this system the arteries and veins run parallel to each other throughout the uterus except for the inner circumferential plexus to which veins are predominantly distributed. The latter division has a delicate arterial system which supplies the mesometrial are of the endometrium. It forms a conglomerate structure along the mesometrial surface of the circular muscle layer. The arrangement of the vessels, especially those in the circumferential division, evidently changes during the oestrous cycle. From the evening of dioestrus II to the evening of pro-oestrus most of the circumferential and radial vessels are enormously dilated and subepithelial capillaries make an elaborate network without blind endings. These changes in the vascular structure are associated with those in the external and internal (or luminal) aspects of the uterus: the uterine horns are markedly swollen and the luminal surface becomes much more irregular due to the indentations in the endometrium. No new vascular formation is found in the uterus throughout the four days cycle.