Part 28

Pelycodus, Cope, Cat. Verteb. Eoc. New Mex., p. 13 (1875).

Tomitherium, Cope, Rep. U. S. Geol. Surv. W. of 100° mer., ii., p. 135 (in part).

Lemuravus, Marsh, Amer. Journ. Sci., 1875, i., p. 239.

{122}This genus is characterised by the second pre-molar having always two roots; the anterior has one root and the third three; the posterior has one external and one internal cusp. Of the true molars, all have two external cusps; the anterior and median have two internal cusps and the posterior has only one; of the lower teeth the posterior pre-molar has an internal cusp and a heel; the next one has no internal cusp; the molars often have the fore inner cusps double; the posterior molar has a strong heel. This genus contains three species, all described by Cope (P. JARROVII, P. TUTUS, P. FRUGIVORUS), with the hind inner cusp of the upper molars distinct from the heel; and P. ANGULATUS, in which that cusp is small and is on the heel. Their remains have been found in the Lower Eocene (Wasatch) beds of New Mexico. P. HELVETICUS has been described from the Upper Eocene of Egerkingen.

GENUS MICROSYOPS.

Microsyops, Leidy, Proc. Acad. Nat. Sci., Philad., 1872, p. 20.

Limnotherium, Marsh, Amer. Journ. Sci., 1871, ii., p. 43 (in part).

This genus is easily distinguished, as Cope points out in his sumptuously illustrated "Vertebrata of the Tertiary Formations of the West," by the absence of the first (anterior) inferior pre-molar, and probably of the superior first pre-molar also. The canine tooth of the lower jaw is very large. The posterior pre-molar has an internal cusp, and the molars two front inner cusps. There are three species, distinguished chiefly by size, M. SPIERIANUS (Cope), very small; M. ELEGANS (Marsh), the largest, with seven teeth succeeding the canine in the lower jaw; and M. SCOTTIANUS (Cope); all from the Eocene of Wyoming.

{123}GENUS HYOPSODUS.

Hyopsodus, Leidy, Proc. Acad. Nat. Sci., Philad., 1870, p. 109.

The present genus is recognised by the front inner cusp of the lower molars being single, and their heel presenting a cusp at its inner hind angle (except in H. acolytus). Of the upper pre-molars, the median and posterior have an internal cusp; and the molars have two outer and two inner cusps with two small intermediate tubercles. There are six species known, from the Wasatch and Bridger beds of Wyoming and New Mexico, of which H. ACOLYTUS is distinguished by having the heel of the anterior and median lower molars without an inner hind cusp. Professor Cope remarks that though the species of this genus are not numerous, individuals of some of them are exceedingly common in the Eocene beds of Wyoming. H. PAULUS and H. MINUSCULUS, Leidy, H. VICARIUS and H. POWELLIANUS, Cope, with H. JURENSIS, Rutimeyer, from the Upper Eocene of Egerkingen, are the best known species.

The genera INDRODON, Cope, from the Lower Eocene Puerco formation of New Mexico, with three cusped upper and four cusped lower molars; OPISTHOTOMUS, APHELISCUS, and SARCOLEMUR, Cope, from the Wasatch of Wyoming; HIPPOSYUS, Leidy; BATHRODON, MESACODON, and STENACODON, Marsh, from the Middle Eocene Bridger beds; are of doubtful affinities.

II. THE MONKEYS AND APES--SUB-ORDER ANTHROPOIDEA.

This Sub-order, though containing animals of much higher organisation than the Lemuroidea, embraces species presenting many different grades of intelligence, and ranging in size from the Pigmy Marmoset, not larger than a small Kitten, to the {124}ponderous Gorilla and the genus Homo. In external characters the Monkeys and Apes have in general a shorter and less Dog-like nose than the Lemurs, thin lips and a more distinct face; while their eyes, situated on the face, are invariably directed forwards, and never outwards, or to the side. The opening of their nostrils is either outward (as in those inhabiting the New World), or downwards (as in the bulk of the Old World species). All of them are covered with hair; the tail may be long, short, or wanting. The proportions of the fore-limbs to the hind- vary much in the different groups. The great toe, as well as the thumb, is (except in a few species) fully opposable, so that in the majority of members of the Sub-order, the foot is as good a prehensile organ as the hand. From this circumstance comes the designation, Quadrumana, or "four-handed," so often applied to these animals. In a few species the thumb is rudimentary or absent, but the fore-finger, the absence of which characterised some of the Lemurs, is always present and well developed, and the corresponding digit in the foot (except in the Marmosets) has a flat nail instead of a claw. The mammæ of the Anthropoidea are always situated on the breast. If we examine the structures underlying the skin, we find that in the skull the orbits are entirely shut in by a bony wall, so that the finger cannot be passed into the temporal depression behind, as could be done in the Lemurine skull, and that the lachrymal foramen opens within the cavity for the eye. In the present Sub-order there is no toothless space in the mid-line of the upper jaw, the incisor teeth being set close together; but there is always a vacuity, except in Man, between the incisors and the canine tooth. The lower canine teeth do not resemble in form the incisors, nor do they protrude horizontally, as in the Lemurs. {125}The two halves of the lower jaw are always co-ossified together, when the animal is full grown. The humerus, or arm-bone, never has an entepicondylar foramen on the inner side of its lower portion, and the bones of the fore-arm (the ulna and radius) are never ossified together, nor are those of the lower leg (the tibia and fibula); so that there is perfect freedom for every movement necessary for grasping and walking, or for rotating the hand or foot on the wrist and ankle.

With regard to the brain, the anthropoid cerebrum, or fore-brain, is greatly convoluted, and differs from that of the Lemurs by its proportionately larger size, the cerebellum, or hind-brain, being as a rule entirely covered by it.

The uterus and structures for the nutrition of the young prior to birth differ greatly in this Sub-order from the conditions existing in the Lemuroidea. The uterus is a simple and not a two-horned sac, and its inner layer, in which the foetal and maternal structures intermingle during the growth of the embryo, is shed after the birth of the young, which is not the case in the Lemurs.

"The resemblance of Monkeys to Man," says Mr. Darwin, "is greatly caused by the relative position of the features of the face. The eyes are arched over; they are separated by a long nose, the end of which in some is very human. The mouth is not carried back, but occupies the same general position as in Man, and the forehead, so often wrinkled, is usually prominent and like that of a child. The likeness is increased by the fact that anger, sorrow, pleasure, and satisfaction, are displayed by the Monkey by nearly similar movements of the muscles and skin, chiefly above the eyebrows and round the mouth. Some few expressions are indeed almost the same, as in the weeping of certain kinds of Monkeys, and in the {126}laughing noise made by others, during which the corners of the mouth are drawn backward and the eyelids wrinkled. In Man the nose is much more prominent than in most Monkeys; but we may trace the commencement of an aquiline curvature in the nose of the Hoolock Gibbon, and this in the Great-nosed Monkey (Nasalis larvatus) is carried to a ridiculous extreme."

In regard to the distribution of the Anthropoidea, excluding Man (Hominidæ), two families (the Hapalidæ and Cebidæ) are known only from the New World; and two others (the Cercopithecidæ and Simiidæ) are exclusively confined to the Old World. No fossil remains of Eastern Hemisphere forms have as yet been found in the Western, or vice versâ, a fact which indicates, doubtless, a separation of great antiquity between the two groups. The various species of these families are to be found chiefly in the warmer regions on both sides of the equator. In the New World some species range as far north as to 20° N. lat. in Mexico; and South, to 30° below the equator. In the Eastern Hemisphere, the Old World species predominate in the tropical and sub-tropical regions; but certain forms have spread as far north as Thibet and Japan, and others have made the high altitudes of the Himalaya Mountains their home; while to the southward they extend in Africa nearly to the Cape of Good Hope. No indigenous species have ever been found in New Guinea, Australia, New Zealand, or in the Pacific, or West Indian Islands.

The Apes of the Old World differ in many important characters from those of the New. Among the former, as already mentioned, the openings of the nostrils are directed downwards, as in Man; the nose is narrow, and the nostrils themselves are set close together, being separated from each other by a thin septum, or partition, of cartilage. On this account, {127}they have received the name of Catarrhine Monkeys (Catarrhini). The New World Monkeys, on the other hand, have the nose flat and the opening of their nostrils directed outwards, and the one nostril widely separated from the other by a broad cartilaginous septum, and they are therefore designated Platyrrhine Monkeys (Platyrrhini).

The dental formula of the Old World forms is I2/2, C1/1, P2/2, M3/3, making a total of thirty-two teeth in all; but those of the Western Hemisphere differ in having invariably three pre-molars, and sometimes two molars, instead of three, so that they possess either thirty-two or thirty-six teeth altogether. There is always a gap, or diastema, in the series of the teeth in front of the upper and behind the lower canines; the latter teeth being taller than the rest. Many of the Catarrhine Apes have large cheek-pouches as well as bare patches, or callosities, often brightly coloured, on the part they apply to the ground when sitting. None of the Platyrrhine group have cheek-pouches or callosities, but in many of them the tail is marvellously prehensile, which is not the case in any of the Old World species. Again, in the Apes of the Eastern Hemisphere, the ear-capsules of the skull have an external bony channel (or meatus) for conveying the sound vibrations into the ear, which is absent in the American species.

As a rule the Platyrrhine Monkeys have the fore-limbs shorter than the hind-, and are more quadrupedal than those of the Old World. Their thumb is also more like a finger than the same digit in their Eastern brethren.

Of the New World Monkeys, the Hapalidæ, or Marmosets, have thirty-two teeth, and the Cebidæ, with several {128}sub-families, have thirty-six teeth. The former include the Marmosets (Hapale) and the Tamarins (Midas). The latter comprise the Capuchins (Cebus), which may be taken as the representative genus of American Monkeys, the Woolly Monkeys (Lagothrix), the Spider-Monkeys (Ateles and the allied Eriodes), the Howlers (Mycetes), the Sakis (Pithecia and Brachyurus), the Night-Monkeys or Douroucolis (Nyctipithecus), and the Squirrel Monkeys or Saimiris (Chrysothrix), with the allied Callithrix.

"The extensive equatorial forests of the Amazon and Orinoco, and their tributaries, constitute par excellence the home of the American Monkeys, but the majority of the genera have a very extended range, appearing in one or more species throughout the greater portion of the tract covered by the entire family. This is more particularly the case with the Sapajous (Cebus), Spider-Monkeys, Howlers, and the species of Callithrix. The range of the species, on the other hand, is not unfrequently very sharply defined, as, for example, when a natural barrier, offering insurmountable obstacles to further migration, suddenly interposes itself. Examples of such limitation, as brought about by the dominant water-courses of the equatorial forests," are numerous. Mr. Wallace cites the case of certain species of Saki Monkey (Pithecia), found on either side of the Amazon river, whose range, either southward or northward, appears to be limited by that river. "The number of species of these American Apes found in, and north of, the Isthmus of Panama is ten, of which only one (Ateles vellerosus) extends into Mexico; Mycetes villosus, the Guatemalan Howler, or 'Mono,' has thus far been found only in Guatemala and Honduras. It is a little surprising that the range of only two of the species--the Black-faced Spider-Monkey (Ateles ater) {129}and one of the Night-Apes (Nyctipithecus vociferans)--extends beyond Colombia, in South America."

"None of the South American Monkeys appear to pass west of the Andean chain of mountains south of Ecuador, and even north of the Peruvian boundary the number of such transgressional forms is very limited. Indeed, even among the wooded slopes, a habitation along the basal line of the mountain axis seems to be much preferred. The greatest altitude at which Monkeys were observed by Tschudi in Peru was 3,000 feet (Lagothrix humboldti); Ateles ater and Cebus robustus were found at 2,500 feet. On the other hand, Salvin and Godman state that in the district of Vera Paz, in Guatemala, the 'Mono' or Howler is most abundant at an elevation of 6,000 feet; and on the Volcano of Atitlan, in the same country, Mr. Salvin found troops of the Mexican Spider-Monkey (Ateles vellerosus) in the forest region of 7,000 feet elevation.

"The range of the Marmosets and Oustitis (Hapalidæ) is nearly co-extensive with that of the Monkeys proper." (Heilbrin.) The Pigmy and the Silky Marmoset range as far north as Mexico.

THE MARMOSETS AND TAMARINS. FAMILY HAPALIDÆ.

Of the New World, or Platyrrhine, Apes, the Marmosets come to be described first, as they have many characters which mark them out as the lowest of the Anthropoidea, and rank them nearer to the Lemuroidea than any of the others. They are specially characterised by having only thirty-two teeth, their dental formula being I2/2, C1/1, P3/3, M2/2. In the actual number of their teeth they agree with their Eastern relations, but with this {130}difference, that in the latter the pre-molars are two, and the molars three, above and below on each side. Their flattened nose, with its wide partition between the nostrils, and their non-prehensile bushy tails, are also distinguishing characters. The face is nude, the ears large and sometimes fringed. Their hind-limbs are proportionately larger and longer than their fore-limbs, while the nails of their fingers and toes are not flattened as in the Old World Apes, but all form sharp curved claws, except on the much shortened great toe. The thumb is elongated and lies parallel, but quite unopposable to, nor indeed is it separable at will from, the rest of the digits. The fore-foot, consequently, "is a mere paw, and the term 'hand' is not applicable to it."... The plantar surface of the hind-foot "is very long, and the digits are very short. It follows from these facts that the term 'quadrumanous' is not applicable in any sense to the Marmosets." (Huxley.) These animals have no callosities over the ischial (or buttock) bones, and no cheek-pouches. In their smooth and rounded skull superciliary ridges are conspicuously absent; and the ear-capsules have, as has been already observed, no external bony canal for conducting sound vibrations to the inner ear. The hyoid bone resembles that of the Lemurs.

This family has been divided into two genera, distinguished from each other only by a variation in the relative length of their incisor and canine teeth, which is so slight as to render it doubtful whether these differences really warrant the generic separation of the two groups. As, however, the distinction has been maintained by nearly all writers upon these animals, the arrangement has been followed here, and the various species of the family will be described as true Marmosets (Hapale) and {131}Tamarins (Midas). They are most numerous in the equatorial forests of South America.