10. The uterus of the females that possess this organ is not of the same nature, nor alike in all, but they differ from each other both in viviparous and oviparous animals. The uterus is double in all those animals in which it is situated near the external organ of generation, one part lying on the right side, the other on the left, but the origin is one, and there is but one os uteri, which is like a very fleshy tube, and in most animals, especially those of a large size, it is cartilaginous. One part of this organ is called the uterus and delphys (whence the word adelphi, brothers), and the vagina and os uteri are called metra. 11. In all viviparous animals, whether bipeds or quadrupeds, the uterus is placed below the diaphragm, as in the human female, the bitch, sow, mare, and cow, and it is the same in all horned animals. At the extremity of the uterus most animals have a convoluted part called the horns; these are not distinct in all oviparous animals; but in some birds they are placed near the diaphragm, and in some fishes below, as in the viviparous bipeds and quadrupeds. But they are thin, membranaceous, and long, so that in very small fish each part of the roe appears as one ovum, as if the fish which are said to have a crumbling roe had but two ova, for it is not one ovum but many, and therefore it may be resolved into many. 12. In the uterus of birds the vagina is below, fleshy and tough, but the part near the diaphragm membranaceous and very thin, so that the eggs appear to be outside the uterus. In large birds the membrane is more conspicuous, and if inflated through the vagina, it swells and enlarges at places; in small birds these parts are not conspicuous. The uterus of oviparous quadrupeds, as the tortoise, lizard, frog, and such like, is of the same nature, for the vagina below is one and fleshy, but the division and the ova are higher up and near the diaphragm. 13. In those apodal creatures which are outwardly viviparous and inwardly oviparous, as the sharks and selachea--[The selachea are apodal, furnished with gills, and viviparous]--the uterus is divided, and as in birds, it commences below and extends towards the diaphragm. The ova are situated between the division, and above near the diaphragm; and the animal is produced from the ovum after this has descended into the open space.