Fam. 2. Cebidae.—The remaining American Monkeys are comprised in the family Cebidae. This is to be distinguished from the last by the fact that there is an additional molar, thus making thirty-six teeth in all. The tail, sometimes very short, is more generally long and highly prehensile, being nude at the extremity, which part is therefore especially prehensile; this state of affairs is often to be seen in animals with prehensile tails. The Cebidae, though for the most part larger than the Marmosets, never approach in size the Old-World Apes.
Typical of the family is the genus Cebus, including the "Capuchin" Monkeys, and consisting of nearly twenty species; the tail, though prehensile, is covered with hair to the tip, a fact which is indicative of a less perfect prehensility than is exhibited in some Monkeys with a naked under surface to the tip of the tail. The thumb is well developed. The genus ranges from Costa Rica to Paraguay. The commonest Monkey which accompanies the street organs of this country is a Cebus. It is a popular delusion that these and other monkeys are purely vegetable-feeding animals. Cebus is in fact particularly fond of caterpillars, as are also the Marmosets.
Allied to Cebus is Lagothrix, the Woolly Monkey, of which L. humboldti is the best-known species, there being indeed but one other. It is a larger and heavier animal than any species of Cebus; and the Hare-like woolliness of the fur suggested its scientific name to its original describer, von Humboldt. It has a perfectly prehensile tail, naked at the tip. The thumb and great toe are well developed. These are purely fruit-eating Monkeys, and are known as "Barrigudos" by the Portuguese of the Amazon country on account of their prominent belly, due apparently to the immense amount of fruit consumed. They are, or were, much eaten by natives.
Brachyteles is a little-known genus, connecting the last with the next genus. The under fur is woolly; the thumb is small or absent. The tail is naked below.
The Spider monkeys, Ateles or Coaitas, have been described as
the most typically arboreal of American monkeys. The use of the prehensile tail can frequently be studied in living examples in the Zoological Society's Gardens. With this "fifth hand" the Monkey feels for a place to grasp, and securely twists its tail round, moving it with the greatest ease from point to point. When the tail is being thus used it is carried erect over the head. The fact that this genus possesses no functional thumb is thought to be associated with the extreme perfection of its adaptability to an exclusively arboreal life. The hand without a thumb can act as an equally efficient hook for suspending the body; and what is useless in nature tends to disappear. These Monkeys have a wide range, extending from Mexico in the north to Uruguay in the south. There are ten species. The flesh of many Monkeys is eaten not only by natives but by Europeans; but the Spider Monkeys are said to furnish the most sapid food of all.
Fig. 265.—Spider Monkey. Ateles ater. × 1⁄12.
The Howling Monkeys, genus Mycetes, have also received the appropriate generic names of Alouatta and Stentor. The former of these two names, indeed, is that which should properly be applied to the genus. But Mycetes is perhaps better known. The "howling" is produced by saccular diverticula of the larynx, larger than those of other American Monkeys, such as Ateles, where, however, they are also developed. The hyoid bones, too,
are enormously enlarged and cavernous, while the jaw—in order to accommodate and protect these various structures—is unusually large and deep. The Howlers are furnished with a fully prehensile tail. The thumb is present. They are described as being the most hideous in aspect of the American Monkeys, and of the lowest intelligence, with which latter characteristic is associated a less convoluted brain than in Ateles, for example. The noise produced by these Monkeys is audible for miles, and is said not to be due to emulation, i.e. not to be comparable to singing or talking, but to serve to intimidate their enemies. The story told of these and other Monkeys with prehensile tails, that they cross rivers by means of a bridge of intertwined Monkeys, is apparently devoid of truth. There are six species, which are Central and South American in range.