ABSTRACT
This chapter deals with the progression of animals based on the mathematical concepts. Aristotle explains that all living things have upper and lower parts, for up and down movements not only in animals but in plants as well; however, in plants the roots are the upper parts, for it is from the roots that nourishment is distributed; it is with the roots that plants take it in, as animals do with their mouths. Since footed creatures stand and support their weight on each of their pairs of opposite legs in turn, it is necessary when one leg steps forward the other should bend. For their opposite legs are naturally equal in length, and that which supports the weight must be erect, that is, perpendicular to the ground. But when one leg goes forward it becomes the hypotenuse and the square on it is equal to the square on the stationary magnitude together with the square on the straight line between.
