His quadrupeds include the mammalia and the quadrupedal reptiles. He divides them into those which are viviparous, and those which are oviparous; the former covered with hair, the latter with scales. Serpents are also scaly, and, excepting the viper, oviparous. Yet all viviparous animals are not hairy; for some fishes, he remarks, likewise bring forth their young alive. In the great family of viviparous quadrupeds also, he says, there are many species (or genera), as man, the lion, the stag, and the dog. He then mentions, as an example of a natural genus, those which have a mane, as the horse, the ass, the mule, and the wild-ass of Syria, which are severally distinct species, but together constitute a genus or family. This introduction to the History of Animals the philosopher seems to have intended, less as a summary of his general views respecting their organization and habits, than as a popular exordium, calculated to engage the attention of the reader, and excite him to the study of nature. Whatever errors it may contain, and however much it may be deficient in strictly methodical arrangement, it is yet obviously the result of extensive, and frequently accurate observation. He then proceeds to the description of the different parts of the human body, first treating of what anatomists call the great regions, and the exterior generally, and then passing to the internal organization. His descriptions in general are vague, and often incorrect. As an example, we may translate the passage that refers to the ear.