There is no circumstance in which the gravid uterus differs more from the unimpregnated than in the size and termination of its blood-vessels. The arteries, both spermatic and hypogastric, are very much enlarged. The hypogastric is commonly considerably larger than the spermatic, and we very often find them of unequal sizes in the different sides. They form a large trunk of communication all along the side of the uterus, and from this the branches are sent across the body of the uterus both before and behind. The cervix uteri has branches only from the hypogastrics, and the fundus only from the spermatics; or, in other words, the hypogastric artery gives a number of branches to the cervix, besides sending up the great anastomosing branch, and the spermatic artery supplies the tube and fundus uteri before it gives down the anastomosing branch on the lateral parts of the uterus. All through the substance of the uterus there are infinite numbers of arteries large and small, so that the whole arterial system makes a general network, and the arteries are convoluted or serpentine in their course.[12] Hardly any of the larger arteries are seen for any length of way upon the outside of the uterus. As they branch from the sides where they first approach the uterus, they disappear by plunging deeper and deeper into its substance. The arterial branches which are most enlarged are those which run towards the placenta, so that wherever the placenta adheres, that part appears evidently to receive by much the greatest quantity of blood, and the greatest number both of the large and small arteries at that part pass through to the placenta, and are necessarily always torn through upon its separation. The veins of the uterus would appear to be still more enlarged in proportion than the arteries. The spermatic and hypogastric veins in general follow the course of the arteries, and like them anastomose on the side of the uterus. From thence they ramify through the substance of the uterus, running deeper and deeper as they go on, and without following precisely the course of the arterial branches. They form a plexus of the largest and most frequent communications which we know of in the vessels of the human body, and this they have in common with the arteries that their larger branches go to, or rather come from, that part of the uterus to which the placenta adheres: so that when the venous system of the uterus is well injected, it is evident that that part is the chief source of returning blood. Here, too, both the large and small veins are continued from the placenta to the uterus, and are always necessarily broken, upon the separation of these two parts. As I know no reason for calling the veins of the uterus sinuses, and as that expression has probably occasioned much confusion among the writers upon this subject, I have industriously avoided it.[13]