14. The difference between the uteri of these fish and others may be studied more accurately in drawings of dissections. Serpents also differ much both among themselves and from other animals, for all serpents except the viper are oviparous; this one is viviparous, though at first internally oviparous, wherefore, in many respects, its uterus resembles that of the cartilaginous fishes. The uterus of the serpent is long, like the body, and descends downwards, beginning from one duct and continuing on either side of the spine as far as the diaphragm, as if each were a passage, in which the ova are placed in order; these ova are not extruded singly, but connected together like a chain. 15. In all animals that are either internally or externally viviparous, the uterus is situated above the abdomen; in all oviparous creatures it is placed below, near the loins. Those that are externally viviparous, but internally oviparous, partake of both characters, for the lower part in which the ova are situated is near the loins, the other part whence the ova are extruded above the intestines. And there is also this difference in the uteri of animals: those which have horns and not teeth in both jaws have cotyledons in the pregnant uterus, and some of those also with teeth in both jaws, as the hare, the mouse, and the bat. But other viviparous animals with teeth in both jaws, and with feet, have a smooth uterus. The embryo is not united to the cotyledon, but to the womb. This is the manner of the internal and external heterogeneous parts of animals. CHAPTER II. 1. Of the homogeneous parts of animals, the blood is common to sanguineous animals; and so is the part in which it is contained, which is called a vein; analogous to these, in exsanguineous animals are the serum and the fibre. That which especially constitutes the body is flesh or its analogue: the bone and its analogue; the spine and the cartilage. Next to this we place the skin, membranes, sinews, hair, nails, and their analogue; after these, adeps, fat, and excrementitious matters; then are fæces, phlegm, and bile, both the yellow and the black.