The genera Protoadapis and Plesiadapis, from the lowest Eocene of Rheims, may not improbably be regarded as primitive Lemuroids. The lower molars are quinquetubercular, and not unlike those of Microsyops; the dental formula of the lower jaw is i 2, c 1, p 3-4, m 3 in the first-named genus, but in the second the dentition is reduced to i ²⁄₁, c ¹⁄₀, p ²⁄₂, m ³⁄₃. In Plesiadapis the lower and the first upper incisor are enlarged, the upper molars (Fig. 334) tritubercular, and the lower quadritubercular. Indrodon, of the lowest Eocene of the United States, resembles Plesiadapis in its tritubercular upper molars, and appears to have a nearly similar dental formula. Mixodectes, of the same deposits, was probably a more or less closely allied type. Pelycodus of the Wasatch Eocene of North America, in which the hallux was not opposable, and Cryptopithecus of the German Eocene, may be regarded as very generalised Lemuroids.

Suborder Anthropoidea.

This suborder includes the whole of the remaining members of the Primates, namely, those animals commonly known as Marmosets, Monkeys, Baboons, and Apes, together with Man himself. The characters by which the Anthropoidea are distinguished as a whole from the Lemuroidea may be summarised as follows. Skull with the orbit separated from the temporal fossa by a vertical plate of bone joining the postorbital bar, and the lachrymal foramen situated within the margin of the orbit. Pollex sometimes rudimentary or absent; second digit of manus always well developed, and that of the pes usually with a flattened nail (not so in Hapalidæ). The cerebral hemispheres of the brain either completely or almost completely cover the cerebellum, and are much convoluted. Uterus not bicornuate. The placenta is deciduate and discoidal; and the allantois is small. There are never abdominal mammæ. As additional points of distinction from the Lemuroidea, it may be mentioned that the anterior cornu of the hyoid is shorter than the posterior; the inner pair of upper incisors are in contact in the middle line; and the transverse portion of the colon extends uninterruptedly across the abdomen.

The Anthropoidea may be divided into the five families—Hapalidæ, Cebidæ, Cercopithecidæ, Simiidæ, and Hominidæ, of which the first and second are confined to the New, and the third and fourth to the Old World.

In noticing some of the salient features in the external and internal structure of the Anthropoidea it will be found convenient to allude to all the members of the first four families as Apes, in contradistinction to Man. In respect to relative size the extremes are found in the Gorilla on the one hand and Hapale on the other; the difference in this respect between these two forms being greater than that between Man and a Squirrel. The relative proportions between the limbs and the body, and also between the fore and hind limbs, are subject to great variation. Thus in Hylobates and Ateles both pairs of limbs are much elongated; in the former case the pectoral being much longer than the pelvic pair (Fig. 335). In other cases, as in the Orang (Fig. 354), while the arms are very long, the legs are short; but in the subfamily Cercopithecinæ both pairs are short and subequal. Only in the Hapalidæ and some of the Cebidæ are the legs proportionately as long as in Man.

The tail is as much as three times the length of the body in Ateles; while in the Simiidæ it is totally absent. In the majority of genera it is long in all the species; but in some cases, as in Macacus, it may be either long, short, or absent in the different species of a single genus.

Equally marked variations occur in the shape of the head. Thus in Ateles it is rounded; while in the Orang it is elevated vertically; in Chrysothrix it is produced posteriorly; and in the Baboons (Cynocephalus) it is characterised by the great production of the muzzle and the terminal position of the nostrils, whereby a characteristic Dog-like form is assumed. The eyes are always directed forwards, and are never more separated from one another than in Man, although, as in Chrysothrix, they may be closer together. They are of very large size in Nyctipithecus, while in the Baboons they are relatively small in proportion to the size of the head. The ears are invariably well developed, and are usually pointed at their postero-superior angle. Those of man are characterised by the soft depending portion known as the “lobule,” of which there is a rudiment in the Gorilla. In the majority of Apes the nose is but very slightly prominent; but it attains an extraordinary development in Nasalis larvatus, and is scarcely less remarkable in Semnopithecus roxellanæ (Fig. 349). Among the Gibbons the Hoolock has a distinctly aquiline nose. The nostrils are terminal in the true Baboons; and while in all the Old World Apes they are approximated, in those of the New World they are separated by a broad septum. With the exception of the Orang, the lips of the Apes are thin.

The pollex makes a nearer approach in form to the human thumb in the Chimpanzee than in any other Ape. Man differs from all the Apes in having the hallux frequently longer instead of shorter than the other digits of the foot. The hallux of the Orang is peculiar in having no nail, but in other cases the nail is flat; the nails of the other digits of the Apes are never quite flat, and in some of the Cebidæ they are decidedly compressed laterally, while in the Hapalidæ they assume the form of sharp and curved claws.

All the Apes have the greater part of the body well clothed with hair. In the Gibbons and the Cercopithecidæ the buttocks have naked ischiatic callosities, which attain their greatest development in Cynocephalus and its allies. The male of the Orang has a well-developed beard, and in Cercopithecus diana there is long hair on the cheeks and chin, while in Macacus silenus the face is surrounded by a fringe of long hair, separated by an interval on the forehead. Long hair is found on the head in Hapale œdipus and in some species of Semnopithecus; while in the Bonnet Monkey (Macacus sinicus) it radiates in all directions from a central point on the vertex. Long hair clothes the shoulders in Cynocephalus hamadryas and Hapale humeralifer; and the end of the tail has a tuft in two species of Cynocephalus and in Macacus sinicus. Many of the African Colobi and some species of the Howlers have very long hair on the flanks; and in Pithecia this development of hair extends to the greater part of the body and the tail, P. satanas also having a long beard. In all the lower Apes the hairs on the arm and forearm are directed towards the hand quite down to the wrist; and the same arrangement obtains in Hylobates. In the other Simiidæ, however (as in man), the points of the hairs of the arm and forearm converge at the elbow. Darwin’s explanation of this peculiarity is that these Apes are accustomed to sit with the arms bent, so that the rain is thus enabled to run off at the elbow.

In one species of Hapale the hair is of a silky texture, and in the South American Eriodes, and Macacus tibetanus (as in all the mammals inhabiting the arid and severe climate of Tibet) it becomes woolly.

The development of very brilliant colours on the naked parts of the body, such as the face, sexual organs, and ischiatic callosities is a marked feature of many of the Cercopithecidæ and some other Apes.

With the exception of the long tail found in most forms, the general structure of the skeleton of the Apes is very similar to that of man, but there are marked differences in the form of the jaws and of the innominate bones. The proportion of the facial to the cranial region of the skull varies with the shape of the head, of which brief mention has already been made; the greatest development of the facial portion being in the Baboons. Curiously enough, some of the lower American Monkeys, and more especially Chrysothrix, have the greatest relative development of the cranial part of the skull of all the Apes; this character being, however, one common to all the smaller representatives of particular groups, and obviously necessary to provide the requisite amount of brain-space. In the convexity of the frontal region of the skull the American forms, and more especially Pithecia, make the nearest approximation to man, and the same is true with regard to the occipital production, which is most developed in Chrysothrix. Most of the Simiidæ exhibit, however, a distinct convexity of the occiput, and thereby differ markedly from the Cercopithecidæ, in which this region is flat. The rotundity of the cranium is obscured in the larger Apes, such as the Orang (Fig. 353) and Gorilla, by the development of prominent bony ridges for muscular attachment; these attaining their maximum in the males of the species last named, where the sagittal crests and the supraorbital ridges are very prominent. The mastoid process is always smaller in the Apes than in Man, and as it diminishes in size the petrosal tends to assume an inflated or bullate condition. The orbits in shape are most like that of Man in the Gorilla; and, in accordance with the size of the eyes, they are of enormous dimensions in Nyctipithecus.

The angle formed by the plane of the foramen magnum with that of the basicranial axis is subject to variation according to the degree of convexity of the occiput, but is generally smaller than in Man, although larger in Chrysothrix. There is an external bony meatus auditorius in Man, the Simiidæ, and the Cercopithecidæ, but none in the Cebidæ and Hapalidæ.

The premaxillæ of the Apes are always large; and, except in the Chimpanzee, the premaxillo-maxillary suture persists until after the permanent dentition has been developed. The nasals are smaller and flatter than in Man, but are largest in Mycetes. The two rami of the mandible are invariably completely ankylosed at the symphysis in the adult. The Siamang (Hylobates syndactylus) is the only ape in which the mandibular symphysis slows a slight projection in front corresponding to the human chin. In Mycetes the angle of the mandible attains an enormous development (Fig. 338) to protect the huge inflated basihyal. The frontal sinuses, though present, in the Simiidæ, are generally replaced in the Cercopithecidæ by a coarse diploë, but they are present in the Cebidæ and Hapalidæ, being especially large in Cebus. In fully adult individuals the cranial sutures become obliterated, the internasal suture disappearing at an early age in the Simiidæ and most of the Cercopithecidæ. As in many Carnivora, the tentorium, or membrane separating the cerebrum from the cerebellum, may become ossified in some of the American forms.

The number of the teeth in the Old World Apes is invariably the same as in Man, namely i ²⁄₂, c ¹⁄₁, p ²⁄₂, m ³⁄₃, total 32; but in the Cebidæ the cheek-teeth are p ³⁄₃, m ³⁄₃, and in the Hapalidæ p ³⁄₃, m ²⁄₂. It is probable that the two pairs of incisors correspond to the first and third of the typical series of three. In all Apes the dental series is interrupted by a diastema, and the canines of the males are large. Man alone has an uninterrupted dental series of a horse-shoe-form, without prominent canines.

According to recent researches the Chimpanzee and some of the other Simiidæ exhibit a more or less close approximation to the sigmoid curvature of the vertebral column which is so characteristic of Man, and there is also some approach to it in the Baboons. The number of dorsal vertebræ in the Apes may vary from eleven, as in some species of Cercopithecus and Macacus, to fourteen in certain forms of Hylobates, and to fifteen in Nyctipithecus. The Cebidæ generally have thirteen; and the same number obtains in the Chimpanzee and Gorilla, while the Orang resembles Man in having but twelve. The lumbar vertebræ show a range in number of from four to seven. In the Simiidæ there are four or five of these vertebræ, the length of the lumbar region being shorter in this family than in the other Apes, with the exception of Ateles. The shortness of the lumbar region in the last-named genus is compensated by the relative length of the dorsal region, as is shown in Fig. 335.

The sacrum is longest in the Simiidæ and Man, its greatest absolute length occurring in the Gorilla, and the relative greatest length being found in Hylobates. The Simiidæ never have less than five, and may have six sacral vertebræ; while in the lower forms there are generally only two or three, although occasionally four in some of the American forms. The Orang and some of the Baboons make the nearest approximation to Man in the marked angle formed at the junction of the sacrum with the lumbar vertebræ. Except in the Simiidæ and Macacus inuus, the number of caudal vertebræ in the Apes always exceeds four, but they may be reduced to five in the Mandrill (Cynocephalus maimon). In Macacus and Uacaria the shortness of the tail is attained by the small size of the vertebræ themselves, the number of which may be from fifteen to seventeen. Other forms usually have from twenty to thirty-three caudals, the latter number occurring in Ateles (Fig. 335), where the tail is relatively the longest. The tail is, however, absolutely longest in Semnopithecus, Colobus, and their allies, the length being partly due to the size of the component vertebræ. Chevron bones are present in all forms having a distinct tail; and, together with other processes for muscular attachment, attain their greatest development in Ateles.

The vertebral processes known as metapophyses and anapophyses, which are generally inconspicuous in Man, and are but small in the Simiidæ, attain a large development in the lower forms. The metapophyses generally commence in the eighth or ninth dorsal, and continue to the anterior caudals, where they gradually merge in the prezygapophyses. The anapophyses, which are most developed in the Cebidæ, project outwards and backwards from one vertebra to embrace the prezygapophyses of the succeeding one. They occur generally in the same region as the metapophyses, but usually cease at the penultimate lumbar, although in some cases they can be traced on to the posterior cervicals and anterior caudals, in the latter region passing into the transverse processes.

In most Apes the sternum is narrow, and consists of a more or less enlarged manubrium, followed by a chain of subequal and antero-posteriorly elongated bones, from three to six in number. In the Simiidæ alone is there a broad sternum, or one consisting of a manubrium, followed by a single bone only, as in Hylobates. The Orang presents a peculiarity, in that the sternum long remains made up of ossifications arranged in pairs, side by side, successively. The true ribs are seven in number on each side in the highest forms, but in Hylobates there are sometimes eight. In Ateles there are sometimes nine pairs. In Hapale the number varies from six to eight, and it is seven or eight in the other genera. The angles of the ribs are never so marked as in Man; although most marked in Hylobates. Pithecia is distinguished by the greater relative breadth of the ribs. In no Ape is the thorax half as broad again as it is deep from back to breast; but in the Simiidæ its transverse diameter exceeds its depth by from about one-fourth to a little under one-third of the latter. In Ateles, and sometimes in Mycetes, the thorax is wider than deep, but in all the rest it is deeper than wide.

In regard to the appendicular skeleton it may be observed that the Gorilla and Orang make the nearest approach to Man in the form of the scapula; and that the supraspinous fossa of this bone is largest in Gorilla and Mycetes, being remarkably small in Simia. The Cebidæ have a distinct suprascapular notch which is often converted by a bar of bone into a foramen; this bar in Mycetes giving rise to a peculiar flat process. The acromion and coracoid processes are most developed in the Simiidæ and Ateles.

The relative length of the fore and hind limbs has been already briefly touched upon. The humerus closely resembles that of Man throughout the suborder; the nearest approximation occurring in the Simiidæ. As in the Lemuroidea, this bone never has an entepicondylar foramen, but in many of the American forms it has a supracondylar perforation. The radius and ulna, like the tibia and fibula, are always perfectly distinct throughout their length; and the hand can be pronated and supinated upon the forearm. Man, the Gorilla, and the Chimpanzee differ from other forms in having no os centrale in the carpus.

The brain of Apes is always much smaller in absolute dimensions than in Man. Thus, according to Professor Mivart,[663] “the cranial capacity is never less than 55 cubic inches in any normal human subject, while in the Orang and Chimpanzee it is but 26 and 27½ cubic inches respectively. The relative size of the brain varies inversely with the size of the whole body, but this is the case in warm-blooded vertebrates generally. The extreme length of the cerebrum never exceeds, as it does in Man, two and a quarter times the length of the basicranial axis. The proportion borne by the brain to its nerves is less in the Apes than in Man, as also is that borne by the cerebrum to the cerebellum. In general structure and form the brain of Apes greatly resembles that of Man. Each half of the cerebrum contains a triradiate lateral ventricle, and though in some Cercopithecidæ the posterior cornu is relatively shorter than in man, it again becomes elongated in the Cebidæ, and in many of the latter it is actually longer relatively than it is in man. The posterior lobes of the cerebrum are almost always so much developed as to cover over the cerebellum, the only exceptions being the strangely different forms Mycetes and Hylobates syndactylus. In the latter the cerebellum is slightly uncovered, but it is so considerably in the former. In Chrysothrix the posterior lobes are much more largely developed relatively than they are in man. The cerebrum has almost always a convoluted external surface. In this group, however, as in mammals generally, a much-convoluted cerebrum is correlated with a considerable absolute bulk of body. Thus in Hapale (and there only) we find the cerebrum quite smooth, the only groove being that which represents the Sylvian fissure. In Simia and Gorilla and Anthropopithecus, on the contrary, it is very richly convoluted. A hippocampus minor is present in all Apes, and in some of the Cebidæ it is much larger relatively than it is in Man, and is absolutely larger than the hippocampus major. Of all Apes, the Orang has a brain which is most like that of Man; indeed, it may be said to be like Man’s in all respects, save that it is much inferior in size and weight, and that the cerebrum is more symmetrically convoluted and less complicated with secondary and tertiary convolutions. If the brain of Simia be compared with that of Gorilla and Anthropopithecus, we find the height of the cerebrum in front greater in proportion in the former than in the latter; also the bridging convolutions, though small, are still distinguishable, while they are absent in the Chimpanzee. Nevertheless this character cannot be of much importance, since it reappears in Ateles, while two kinds of the genus Cebus (so closely allied as to have been sometimes treated as one species) differ strangely from each other in this respect. The corpus callosum, in Apes generally, does not extend so far back as in Man, and it is very short in Pithecia. In the Orang and Chimpanzee there are, as in Man, two corpora albicantia, while in the lower Monkeys there is but one. The vermis of the cerebellum is larger in the Cebidæ than in the Simiidæ and Cercopithecidæ. In all Apes below the Simiidæ each lateral lobe of the cerebellum gives off a small lobule, which is received into a special fossa of the petrous bone. Certain prominences of the medulla oblongata, termed corpora trapezoidea, which are found in lower mammals, begin to make their appearance in the Cebidæ.”

The organs connected with the functions of alimentation, circulation, and excretion, as well as the muscles, conform generally to the type obtaining in Man, of which full description will be found in works on human anatomy. The tongue is longer in Apes than in Man; and a uvula is generally present, although rudimentary in the Cebidæ. The peculiar sacculation of the stomach in the subfamily Semnopithecinæ has been already mentioned; this sacculation is most developed at the cardiac extremity, where it somewhat resembles a colon spirally coiled. In Hylobates the stomach is very like that of Man, differing only in the more elongated and distinct pylorus. Pithecia has a more globular stomach, while in Hapale the cardiac and pyloric apertures are approximated. The intestine of Apes is devoid of valvulæ conniventes, and it is only in Man and the Simiidæ that the colon is furnished with a vermiform appendage. The colon varies from a fully sacculated form in Hylobates to a smooth one in Cebus.

The liver of Apes is subject to a considerable amount of variation. In the Simiidæ it comes more or less close to the human type; that of the Orangs being usually divided only into two principal lobes by the umbilical vein, and showing no trace of lateral fissures. In the Gorilla these fissures are present, so as to produce right and left lateral and central lobes. Hylobates has a liver (Fig. 352) which perhaps is nearer to the human than that of any of the other Simiidæ. In the Cercopithecidæ the liver differs from that of the Simiidæ by the deeply cleft lateral fissures, and has a comparatively small and pointed caudate lobe. The enormous size of the stomach in Colobus causes the liver to be very narrow, and pushed to the left side. The liver of the Cebidæ (Fig. 336) and Hapalidæ, in addition to the deeply cleft lateral fissures, is characterised by the great size and quadrangular form of the caudate lobe (c), which attains its maximum development in Ateles. The gall-bladder is always present.

The larynx is in many Apes furnished with sac-like appendages, which are variable in different species as regards number, size, and situation. They may be dilatations of the laryngeal ventricle, as in Simia, Gorilla, and Anthropopithecus, or they may open above the false vocal chords so as to be extensions of the thyro-hyoid membrane, as in Hylobates. There may be but a single median opening in the front part of that membrane at the base of the epiglottis, as in the Cercopithecidæ. There may be a single median opening at the back of the trachea, just below the cricoid cartage, as in Ateles; there may be but a single sac, or there may be five, as sometimes in Mycetes. These may be enormous, meeting in the middle line in front and extending down to the axillæ, as in the Gorilla and Orang. A sac may occupy the cavity of the expanded body of the hyoid, as in Mycetes.

The hyoid has its basilar part generally somewhat more convex and enlarged than in Man; but in Mycetes it becomes greatly enlarged and deeply excavated, so as to form a great bony bladder-like structure. The posterior cornua of the hyoid (thyrohyals) are never entirely absent, but the anterior or lesser cornua may be so, as in Mycetes. The anterior cornua never exceed the posterior cornua in length; but they may be (e.g. in Cercopithecus) more largely developed relatively than in Man, and may even be jointed, as in Lagothrix.

The lungs have generally the form of those of man; but the right lung may have four lobes, as in Hylobates. The great arterial trunks in Simia, Gorilla, and Anthropopithecus are arranged as in Man. In Hylobates and the lower Apes, however, the left carotid artery may take its origin from the innominate artery.

In regard to their distribution in time the earliest record that we as yet have of the occurrence of Apes is in the Middle Miocene of Europe, where forms are met with apparently so closely allied to some of the higher existing types that it is evident we must look much farther back before we can get any clue to the origin of the suborder. Since all the known fossil Old World Apes are referable to the Simiidæ or Cercopithecidæ, and no representatives of these families have been obtained from the Tertiaries of America, it would appear that the distinction of the Apes of the Old World from those of the New is of very old standing.

At the present day Apes are mainly confined to tropical and subtropical regions. In the Old World Macacus inuus is found as far north as Gibraltar, M. tibetanus and Semnopithecus roxellanæ inhabit western Tibet, while in Japan we have M. speciosus. In the New World one species of Ateles is known to occur as far north as latitude 19° in Southern Mexico, and may range a few degrees higher. To the southward species are found near the Cape, in Timor, and the Malay Archipelago; while in America they range in Brazil and Paraguay to about latitude 30°. The Tibetan species are found at a very high elevation; and in the outer Himalaya the Langurs (Semnopithecus) may be seen in winter and spring leaping from bough to bough of snow-covered pines.

Apes are very abundant in the Ethiopian and Oriental regions, as well as in that part of America which extends from Panama to Southern Brazil. Ceylon, Borneo, Sumatra, and Java may be mentioned as islands where Ape-life attains great development; but they are unknown in Madagascar and the West Indian Islands, and of course in the Australasian region.

We have already alluded to the circumstance that while the Simiidæ and Cercopithecidæ are exclusively confined to the Old World, the Cebidæ and Hapalidæ are equally restricted to the New, and we may accordingly proceed to notice a few points in relation to generic distribution. Of the larger Simiidæ the Gorilla and Chimpanzee are confined to Equatorial Africa, and the Orang to Malayana; but there is evidence of the former existence of a species of Chimpanzee (Anthropopithecus) and not improbably of an Orang (Simia) in Northern India. The Gibbons (Hylobates) are now exclusively Oriental. Europe has only Macacus inuus of Gibraltar, also found in Africa north of the Sahara, and therefore strictly Palæarctic in distribution. The Ethiopian region includes in the Cercopithecidæ the genus Colobus (the African analogue of Semnopithecus), Cercopithecus, and the Baboons (Cynocephalus, etc.) The Baboons range, however, into Arabia and Syria, and also existed during the Pliocene epoch in Northern India. Semnopithecus and Macacus are very characteristic of the Oriental region; but, as already mentioned, outlying species extend into various parts of the Palæarctic region. Macacus has indeed a very wide distribution, extending from Gibraltar and North Africa to Japan. The allied Cynopithecus, represented only by C. niger of Celebes, approximates to the Baboons; while the one species of Nasalis is peculiar to Borneo. Remains of Semnopithecus and Macacus occur in the Tertiaries of India and Europe, which also yield allied extinct types noticed in the sequel.

In America, north of Panama, the genera known to be represented are Chrysothrix, Nyctipithecus, Cebus, Ateles, Mycetes and Hapale in Veragua; Nyctipithecus, Cebus, Ateles, and Mycetes in Costa Rica and Nicaragua; Ateles and Mycetes in Guatemala; and Ateles in Southern Mexico. Brazil is the headquarters of the American Apes; but different portions of that vast region have a somewhat distinct Ape fauna. Thus the genus Eriodes appears in South-Eastern Brazil to represent the species of Ateles inhabiting the more northern and western parts of the empire. Southwards, the genera Cebus, Mycetes, Chrysothrix, and Callithrix extend farthest; but they do not probably all extend to the farthest limit yet known, namely 30° S. The species found farthest south are Mycetes caraya, Cebus fatuellus, and Callithrix personatus.

Family Hapalidæ.

Dentition: i ²⁄₂, c ¹⁄₁, p ³⁄₃, m ²⁄₂; total 32. No bony external auditory meatus, a broad internarial septum, and no cheek-pouches. Tail non-prehensile; no ischiatic callosities. Pollex not opposable; a long, curved, and pointed claw to all the digits except the hallux.

This family, which includes the smallest representatives of the suborder, commonly known as Marmosets, is confined to the New World. In addition to the diagnostic characters given above, it may be mentioned that the pollex is elongated and the hallux very small, while the pectoral limbs are not longer than the pelvic pair; and the tail is long and more or less thickly covered with elongated hairs.

The dentition of the Marmosets sufficiently distinguishes them from all other members of the suborder, although they are evidently nearly allied to the Cebidæ. The small size of the hallux, and the total incapacity of the pollex to oppose itself in the least degree to the other digits, as well as the presence of claws on all the digits of the manus, are, however, equally characteristic features. These animals (Fig. 337) are not larger than Squirrels, and are of active arboreal habits, living in small companies, and adding insects to the ordinary fruit diet. Frequently, as in the figured species, the head is furnished on either side with a long tuft of hair projecting outwards and backwards. They give birth to as many as three young ones at a time, and thereby differ from all other members of the suborder, in which one is the normal number. They are divided into two genera, according to the proportionate size of the lower canine to the incisors; but some species present an intermediate condition, so as to render this distinction of somewhat doubtful value.

Hapale.[664]—Lower canine not longer than the incisors. A number of species have been described, among which may be mentioned H. jacchus, H. albicollis, H. aurita, and H. humeralifer. Remains of species of this genus have been found in the cavern-deposits of Brazil.

Midas.[665]—Lower canine considerably longer than the incisors. No less than twenty-four species of this genus have been named, among which the Silky Marmoset (M. rosalia) of Columbia, the Pinche Monkey (M. œdipus) of South-Eastern Brazil, and the Golden Marmoset (M. chrysoleucas, Fig. 337) are well-known types.

Family Cebidæ.

Dentition: i ²⁄₂, c ¹⁄₁, p ³⁄₃, m ³⁄₃; total 36. Tail frequently prehensile; digits with nails; other characters as in the Hapalidæ.

The members of this American family are at once distinguished by the dental formula, which is numerically higher than in any other Apes. The various species range over the whole of tropical America, but are most abundant in the dense forest regions of Brazil, where they live a completely arboreal life, to which the prehensile tails of many of them are so specially adapted. They are in most respects closely allied to the Hapalidæ, but the pollex diverges somewhat from the plane of the other digits; while the retention of the third molar is a very distinctive feature. None of the species attain the dimensions of the larger Cercopithecidæ of the Old World. The genera are usually arranged in five subfamilies.

Subfamily Mycetinæ.—Lower incisors vertical; hyoid bones enormously inflated; tail long and prehensile, naked beneath at the end; pollex well developed.

Mycetes.[666]—The sole representatives of this subfamily are the well-known Howling Monkeys, all of which are included in the genus Mycetes. They are of more bulky build, and have more produced muzzles than the other members of the family. The truncated occipital region, and the extraordinary development of the rami of the mandible, especially of their angular and ascending portions, are the chief peculiarities by which the skulls (Fig. 338) of the members of this genus are characterised. The last named character, which is more marked in the male than in the female sex, is related to the enormous size of the vocal organs, which the rami of the mandible enclose and protect. The inflated hyoid bone, which forms a deep cup, is shown in the figure. The Howlers are subject to great individual and sexual variation of colours, so that the discrimination of species from local races is difficult. In one species the male is black and the female straw-coloured; and several of the species have bright red or golden hair on the flanks. In disposition these creatures are sluggish and stupid, but their chief characteristic is their prodigious power of voice. Mr. Bates, in his Naturalist on the Amazons, observes that “when Howlers are seen in the forest there are generally three or four of them mounted on the topmost branches of a tree. It does not appear that their harrowing roar is emitted from sudden alarm; at least it was not so in captive individuals. It is probable, however, that the noise serves to intimidate their enemies.”

Several species have been described, the Red Howler (M. seniculus) and the Ursine Howler (M. ursinus) being well-known forms. Remains of this genus probably referable to existing types are found fossilised in the cavern-deposits of Brazil. An allied fossil form from the South American Pleistocene has been described as Protopithecus.

Subfamily Pitheciinæ.—Lower incisors inclined forward at their summits; hyoid bone normal; tail long or short, non-prehensile; pollex well developed. Two genera are included in this subfamily, readily distinguished by the length of the tail.

Pithecia.[667]—The Sakis, as the representatives of this genus are commonly termed, are readily characterised by the length of the tail; the angle of the mandible is expanded, although less so than in Mycetes. A number of species have been described, the Black Saki (P. satanas) of the Lower Amazons, being one of the best known. While some species, like P. hirsuta, have long hair covering the whole of the head, body, and tail, in others only the head, or the cheeks and chin, are so clothed.

Uacaria.[668]—The Uakari Monkeys differ from all the other Cebidæ by their short Baboon-like tail. The Bald Uakari (U. calva) of the Rio Negro, and the closely allied U. rubicunda of the Upper Amazons, are remarkable for their scarlet face, which forms a striking contrast to the long, silky, whitish hair covering the body. According to Mr. Bates, the Uakaris live in forests which are inundated during a great part of the year, and never descend to the ground; they appear to be rare and of local distribution. The third species, U. melanocephala, differs considerably from both the others. The cæcum of U. calva, according to Mr. F. E. Beddard, measures upwards of “10 inches along the greater curvature; it is separated from the colon by a very marked constriction; it is not sacculated, and when fully distended with air is curved on itself into a little less than a circle; it is furnished with a well-developed median frenum carrying blood-vessels.” A similar type of cæcum is also found in Callithrix and Pithecia.

Subfamily Nyctipithecinæ.—Lower incisors vertical; hyoid normal; tail long, non-prehensile; pollex well developed.

Three genera are included in this subfamily, the species being partly insectivorous.

Callithrix.[669]—Head small, depressed, and not elongated; nares widely separated; canines small; angle of mandible expanded as in Pithecia; tail with long hair.

This genus comprises several small species, mostly from Brazil and the Amazons, and commonly known as Teetees, one of the best-known species (C. moloch, Fig. 339) being represented in the accompanying woodcut. The smaller eyes and the more widely separated nostrils distinguish them from Nyctipithecus; while the small canines and the bushy tail readily mark their distinction from Chrysothrix. Remains of Callithrix have been found in the Brazilian caves.

Chrysothrix.[670]—Head greatly elongated; orbits large and closely approximated; canines well developed; tail with comparatively short hair.

The small Squirrel Monkeys, of which four species have been described, are characterised by the great backward projection of the occipital region of the skull, and by orbits approximating in size to those of the next genus.

Nyctipithecus.[671]—Head rounded; orbits very large, separated by a narrow septum; nares somewhat approximated.

The Douroucoulis (Fig. 340), as the members of this genus are called, are of nocturnal habits, in association with which the eyes are of enormous dimensions, as in the Lemuroid genus Loris. The following account, of two species of this genus is taken from Mr. Bates’s Naturalist on the Amazons: “They sleep all day long in hollow trees, and come forth to prey on insects and eat fruit only in the night. They are of small size, the body being about a foot long, and the tail 14 inches, and are thickly clothed with soft gray and brown fur, similar in substance to that of the Rabbit. Their physiognomy reminds one of the Owl or Tiger-Cat; the face is rounded and encircled by a ruff of whitish fur; the muzzle is not at all prominent; the mouth and chin are small; the ears are very short, scarcely appearing above the hair of the head; and the eyes are large and yellowish in colour, imparting the staring expression of nocturnal birds of prey. The forehead is whitish, and decorated with black stripes, which in one of the species (N. trivirgatus) continue to the crown, and in the other (N. felinus) meet on the top of the forehead. N. trivirgatus was first described by Humboldt, who discovered it on the banks of the Cassiquiare, near the headquarters of the Rio Negro.”

Subfamily Cebinæ.—Lower incisors vertical; hyoid bone normal; tail long and prehensile; pollex present or absent.

This subfamily includes the typical members of the family, which are arranged in four genera.

Ateles.[672]—Form slender; limbs very long; fur not woolly; pollex absent; tail naked beneath distally; nails not much laterally compressed and pointed.

This genus includes the well-known Spider Monkeys (Fig. 341), which by their long limbs and tail are admirably adapted to a purely arboreal life, although they lack the active and agile habits of the Old World Gibbons. The tail with the under surface of its extremity naked affords the most completely prehensile type of this organ, and can sustain the weight of the whole body. Objects are not unfrequently grasped by it and brought within reach of the hand or mouth. Owing to the absence of the pollex the power of grasping is very imperfect in the hand. At least fourteen species of this genus have been described, among the best-known being A. melanochir (Fig. 341), A. paniscus of Guiana, A. geoffroyi of Central America, A. ater of Eastern Peru, and A. hybridus of Colombia.

Eriodes.[673]—Form slender; limbs very long; fur woolly; internasal septum narrower than usual in the family; pollex rudimentary; tail naked beneath distally; nails exceedingly compressed laterally, and pointed.

This genus is represented by three species from South-East Brazil, which, while closely allied to the true Spider Monkeys, differ by their woolly hair, the narrow internasal septum, the presence of a rudimentary pollex, and the great compression of the nails. The species are E. arachnoides, E. hemidactylus, and E. hypoxanthus.

Lagothrix.[674]—Form rather robust; limbs moderate; fur woolly; pollex well developed; tail distally naked beneath.