_A hand_, unlike a foot, has one of the digits, called a thumb, placed opposite the other four digits that it may be used in grasping. Two-handed man and four-handed apes and monkeys are usually placed in one order, the _Primates_, or in two orders (see table, page 193). The lowest members of this order are the _lemurs_ of the old world. Because of their hands and feet being true grasping organs, they are placed among the primates, notwithstanding the long muzzle and expressionless, foxlike face. (Fig. 402.) Next in order are the _tailed monkeys_, while the _tailless apes_ are the highest next to man. [Illustration: FIG. 403.--BROAD-NOSED MONKEY. × ¹⁄₁₀. America.] [Illustration: FIG. 404.--NARROW-NOSED MONKEY. × ¹⁄₁₂. Old World.] [Illustration: FIG. 405.--GORILLA. (Size of a man.)] The _primates of the New World_ are all monkeys with long tails and broad noses. They are found from Paraguay to Mexico. The _monkeys and apes of the Old World_ have a _thin partition_ between the nostrils, and are thus distinguished from the monkeys of the New World, which have a _thicker partition_ and have a broader nose. (Figs. 403, 404.) The monkeys of America all have _six molar teeth_ in each half jaw (Fig. 352); the monkeys and apes of the Old World have thirty-two teeth which agree both in number and arrangement with those of man. Which of the primates figured in this book appear to have the arm longer than the leg? Which have the eyes directed forward instead of sideways, as with cats or dogs? Nearly all the primates are _forest dwellers_, and inhabit warm countries, where the boughs of trees are never covered with ice or snow. Their _ability in climbing_ serves greatly to protect them from beasts of prey. Many apes and monkeys are able to assume the upright position in walking, but they touch the ground with their knuckles every few steps to aid in preserving the balance. [Illustration: FIG. 406.--CHIMPANZEE.] The _Simians_ are the highest family of primates below man, and include the gorilla, chimpanzee, orang, and gibbon. Some of the simians weave together branches in the treetops to form a rude nest, and all are very affectionate and devoted to their young. How are apes most readily distinguished from monkeys? (Figs. 401, 406.) The study of man as related to his environment will be taken up in detail in the part called Human Biology. We will there examine the effect upon man’s body of the rapid changes since emerging from savagery that he has made in food eaten, air breathed, clothing, and habits of life. [Illustration: FIG. 407.--ANATOMY OF RABBIT.