BOOK III.--The third book commences with a description of the internal

organs, beginning with the generative system. A considerable portion of the book is devoted to the course of the veins; and Aristotle quotes from other writers, as well as states the result of his own observations. He then describes the nature of other constituent parts of the body, sinews, fibres, bone, marrow, cartilage, nails, hoofs, claws, horns, and beaks of birds, hair, scales, membranes, flesh, fat, blood, marrow, milk, and the spermatic fluid.