Quadrumana (Lat., from quatuor, four, and manus, hand), a division of the mammalia embracing the lemurs and monkeys or apes, and forming the highest order of Owen's subclass gyrencephala, so called from the generally prehensile nature of their four extremities. Although, on anatomical grounds, the term quad-rumanous cannot be considered as strictly applicable to the members of this extensive order, it is nevertheless retained by the majority of naturalists in contradistinction to bimanous (two-handed), as restricted to man alone. The restoration of the Linnaean term primates (limited so as to exclude the cheiroptera) has of late been advocated by Prof. Huxley, as more conformable to the true nature of structural affinities, a view in which he has been sustained by St. George Mivart. This order, which has been conveniently divided into the three families of strepsirrhini, platyrrhini, and catarrhini, may be briefly defined as follows: Animals with a deciduate, discoidal placenta; clavicles complete; orbital ring completely circumscribed, and usually separated by an osseous septum from the temporal fossa; pollex (when present) often, and hallux generally opposable, the latter provided with a flat nail (except in orang, in which the nail is often wanting); cerebral hemispheres well developed and strongly convoluted, covering the cerebellum (except in mycetes and certain genera of the lemuridoe, where the cerebellum is naked, and in the marmoset, where the external gyri and sulci are almost entirely wanting); stomach in most cases simple (complex in semnopithecus and colobus) and furnished with caecal appendages; teeth never in an unbroken series, but separated by a diastema. - The strepsirrhini (lemurs, aye-ayes, loris, galagos, potos, and in-dris) constitute the lowest family of the order, and inhabit portions of Africa, Madagascar, and some of the Asiatic islands.
They are characterized by the twisted nature of their nostrils, and by the presence of a claw on the second digit of the foot. The aye-ayes (cheiro-mys), which seem to connect the lemurs with the lower rodents, form an abnormal group by themselves, by reason of the true rodent type of their dentition, which is, incisors 1/1-1/1, canines 0/0, premolars 1/0-1/0, and molars 3/3-3/3=18. The chisel-shaped incisors, moreover, agree with those of the rodents in growing from persistent pulps, but differ in being entirely invested with a coat of enamel. The platyrrhini, American monkeys, are distinguished from the catarrhini, or monkeys of the old world, by several well marked characters, the most prominent of which is the broader development of the nasal septum. They also differ from them in the universal presence of a tail, which is generally prehensile, and in their dental formula, which is, incisors 2/2-2/2, canines 1/1-1/1, premolars 3/3-3/3, and molars 3/3-3/3=36. The marmosets form a sole exception to the general rule of dentition, in possessing but two molars in each side of both jaws, thereby reducing the total number of teeth to 32. The catar-rhini have the dental formula corresponding to that of man, namely, incisors 2/2-2/2, canines 1/1-1/1, premolars 2/2-2/2, and molars 3/3-3/3=32. In this family the meatus auditorius externus is osseous, and the pollex is, with one exception (colobus), always opposable, circumstances which would be by themselves almost sufficient to separate the monkeys of the old from those of the new world.
The catarrhini have been divided into the subfamilies cynomorplia and anthropomorpha. The former (baboons, macaques, &c), which are essentially quadrupedal, are all possessed of ischial callosities, and in the majority of cases cheek pouches, serving as temporary receptacles for food, are present; the latter comprise the anthropoid apes, which, like the gorilla, assume a semi-erect attitude. - The skull in the quadrumana presents an extraordinary amount of divergence. It rarely assumes the rounded form observed in man, owing to the disproportionate size of the face as compared to that of the brain case. The facial portion attains its greatest development in the dog-faced baboon (cynocephalus) of Africa, where the jaws are prodigiously extended. The squirrel monkey (chrysothrix) of South America presents the opposite extreme, in having the face relatively smaller even than in man. In no instance does the absolute size of the brain approach that of the human subject. The cranial capacity, which is seldom as much as 26 or 27 cubic inches (orang and chimpanzee), reaches its maximum, 35 inches, in the gorilla.
The number of vertebrae entering into the composition of the dorso-lumbar region of the spinal column is 17 in the orang, chimpanzee, and gorilla, 18 in ateles and hylobates, 22 in nyctipithe-cus, and 19 in the remaining monkeys; in the lemurs the number varies from 19 (typical) to 24 in stenops tardigradus. The caudal vertebrae are susceptible of a much greater variation, ranging from 3 in the Barbary ape to 33 in the spider monkey. The muscular system of the quadrumana closely resembles that of man, differing most widely in the long-tailed monkeys, where the muscles answering to the coccygeal in the human form are very greatly developed. The respiratory system presents some curious modifications, especially noticeable in the singular structure of the larynges. These are in many cases provided with air sacs, numbering five in the howlers, whereby the intensity of sound is greatly increased. - The quadrumana are very extensively distributed over the tropical regions of both hemispheres. The catarrhini inhabit almost the entire continent of Africa, a large portion of southern Asia, and most of the islands constituting the Indian archipelago.
It is a singular fact that Papua, an island rich in animal and vegetable forms, and presenting climatal and terrestrial conditions almost analogous to those of Borneo, Sumatra, or Java, should be entirely destitute of a monkey population; nor is it less remarkable that Australia has thus far furnished not a single representative of this family. But one species, the macacus inuus, is found native of Europe. Brazil is preeminently the home of the American monkeys, which however extend from Mexico to the 30th parallel of S. latitude. The West India islands present the same peculiarity as Papua. The limit of the vertical distribution of the quadrumana appears to be about 11,000 ft. - No unequivocal remains of a monkey have as yet been discovered in any formation dating anterior to the miocene. The best known fossil forms are the dryopithecus and pliopithecus, from the fresh-water deposits of France. It is worthy of remark that the present divisions of catarrhini and platyrrhini seem to have been as clearly defined in former ages as they are now, no representative of either family having as yet been found in the hemisphere other than that to which it is peculiar. - The exact position of the quadrumana is still unsatisfactorily determined.
Their close relationship to the bimana is obvious, but, as Mivart remarks, it may be doubted whether, if the animal man had never existed, the highest point in the scale of perfection would have been conceded to the apes. The transition to the quadrumana from the lower orders is effected through the galeopithecus, a lissencephalous insectivore, inhabiting the Indian archipelago. - For detailed descriptions of the different families, see the articles Ape, Aye-Aye, Baboon, Chimpanzee, Gibbon, Gorilla, Lemur, Lori, Macaque, Marmoset, Monkey, and Orang-Outang. See also Owen, "Anatomy of Vertebrates," vols. i. and ii. (1866-'8); Huxley, "Man's Place in Nature" (1863), and "Anatomy of Vertebra-ted Animals" (1872); Darwin, "Descent of Man" (1871); and the article "Ape" by St. George Mivart in vol. ii. of the "Encyclopaedia Britannica" (9th ed., 1875).