The vast family of simians has perhaps the widest range of types of any single family of animals. Beginning with the great apes, which in size, form, and structure so closely resemble man, we descend the scale until it ends in the lemurs, which are almost on the level of rodents. The descent is so gradual that it is difficult to draw a line of demarcation at any point between the two extremes. There is now, however, an effort being made to separate this family into smaller and more distinct groups; but the lines between them are not sharply drawn, and the literature of the past has a tendency to retard the effort. But we shall not here assume to discuss the problems with which zoölogy may in the future have to contend; we shall accept the current system of classification and proceed along that line. In the language of the masses all the varied types that belong to the simian family are known as _monkeys_. This term is so broad in its application as to include many forms which are not to be considered in this work, and many of them should be known under other names. Some of these resemble man more than they resemble each other. By the word _monkey_, we mean to refer only to those of the simian tribe that have long tails and short faces, while the word _baboon_ refers only to the dog-like forms having tails of medium length and long projecting faces. The term _ape_ will be applied only to those having no tails at all. While all of these animals are called simians, they are not all monkeys. The simian family is divided into two great classes, known as _old world monkeys_ and _new world monkeys_. The chief point of distinction is in the structure of the nose. All of the monkeys belonging to the old world stock have long, straight noses with vertical nostrils, separated by a narrow thin wall, or septum, and from this fact they are technically known as _catarrhini_. The new world stock have short, flat noses with oblique nostrils set wide apart, and on this account they are known as _platarrhini_. There are many other marks that distinguish genera and species, but these are the two grand divisions of the simian race. We shall not here attempt to classify the many genera and species of either of these divisions. But we shall point out some of the most salient anatomical features of men and apes, and then those of monkeys.