CHAPTER VII

THE SUBCLASS EUTHERIA AND THE ORDER EDENTATA

The whole of the remaining groups of mammals are included in a single subclass, known by the names Eutheria, Monodelphia, or Placentalia.[87] The one distinctive feature they have in common (from which the last-mentioned name is derived) is the presence of an allantoic placenta by means of which the fœtus is nourished within the uterus of the mother. Throughout the entire subclass, as a general rule, the urino-genital organs open quite independently of the rectum; the corpus callosum of the brain is well developed; the mandible does not show a marked inflection of its angle; and distinct epipubic bones are not attached to the anterior margin of the pubic symphysis. In those cases where there is a heterodont and diphyodont dentition the dental formula can be reduced to some modification of the one given on p. 25, there being only one known genus where four true molars occur, and even that not invariably. As in the Metatheria, the coracoid is reduced to a mere appendage of the scapula, and the acetabular cavity of the pelvis is imperforate. While the survivors of the other subclasses have probably been for a long time in a stationary condition, these have, as there is already good evidence to show throughout all the Tertiary geological age, and by inference for some time before, been multiplying in numbers and variations of form, and attaining higher stages of development and specialisation in various directions. They consequently exhibit far greater diversity of external or adaptive modification than is met with in either of the other subclasses,—some being fitted to live as exclusively in the water as fishes, and others to emulate the aerial flight of birds.

To facilitate the study of the different component members of this large group, it is usual to separate them into certain divisions which are called “orders.” In the main zoologists are now of accord as to the general number and limits of these divisions among the existing forms, but the affinities and relationships of the orders to one another are far from being understood, and there are very many extinct forms already discovered which do not fit at all satisfactorily into any of the orders as commonly defined.

Commencing with the most easily distinguished, we may first separate a group called Edentata, composed of several very distinct forms, the Sloths, Anteaters, and Armadillos, which under great modifications of characters of limbs and digestive organs, as well as habits of life, have just enough in common to make it probable that they are the very specialised survivors of an ancient group, most of the members of which are extinct, although the researches of palæontology have not yet revealed them to us. The characters of their cerebral, dental, and in many cases of their reproductive organs show an inferior grade of organisation to that of the generality of the subclass. The next order, about the limits of which there is no difficulty, is the Sirenia,—aquatic vegetable-eating animals, with complete absence of hind limbs, and low cerebral organisation,—represented in our present state of knowledge by but two existing genera, the Dugongs and Manatees, and by a few extinct forms, which, though approaching a more generalised mammalian type, show no special characters allying them to any of the other orders. Another equally well-marked and equally isolated, though far more numerously represented and diversified order, is that of the Cetacea, composed of the various forms of Whales, Dolphins, and Porpoises. In aquatic habits, external fish-like form, and absence of hind limbs, they resemble the last, though in all other characters they are as widely removed as are any two orders among the Eutheria.

All the remaining orders are more nearly allied together, the steps by which they have become modified from one general type being in most cases not difficult to realise. Their dentition especially, however diversified in detail, always responds to the formula already alluded to, and, although the existing forms are broken up into groups in most cases easy of definition, the discoveries already made in palæontology have in great measure filled up the gaps between them.

Very isolated among existing Eutheria are the two species of Elephant constituting the group called Proboscidea. These, however, are now known to be the survivors of a large series of similar animals, Mammoths, Mastodons, and Dinotheres, which as we pass backwards in time gradually assume a more ordinary or generalised type; and the interval which was lately supposed to exist between even these and the rest of the class is partially bridged over by the discovery in American Eocene and early Miocene formations of the gigantic Dinocerata, evidently offshoots of the great group of hoofed animals, or Ungulata, represented in the actual fauna by the Horses, Rhinoceroses, Tapirs, Swine, and Ruminants. Almost as isolated as the Proboscidea among existing mammals are the few small species constituting the family _Hyracidæ_, and in their case palæontology affords no help at present, and therefore, pending further discoveries, it has been thought advisable in most recent systems to give them the honour of an order to themselves, under the name of Hyracoidea. But the number of extinct forms already known allied to the Ungulata, though not coming under the definition of either of the two groups (Artiodactyla and Perissodactyla) under which all existing species range themselves, is so great that either many new orders must be made for their reception or the definition of the old order Ungulata so far extended as to receive them all, in which case both Proboscidea and Hyracoidea may be included within it. Again, the Rodentia or gnawing animals—Rabbits, Rats, Squirrels, Porcupines, Beavers, etc.—are, if we look only at the present state of the class, most isolated. No one can doubt what is meant by a Rodent animal, or have any difficulty about defining it clearly, at least by its dental characters; yet our definitions break down before the extinct South American _Typotherium_, half Rodent and half Ungulate, which leads by an easy transition to the still more truly Ungulate _Toxodon_, for the reception of which a distinct order (Toxodontia) has been proposed. It has also been suggested that the Rodents are connected by some of the extinct Tillodontia (or Tæniodontia) with the Edentates. The Insectivora and the Carnivora again are at present quite distinct orders, but they merge into one another through fossil forms, and are especially connected by the large group of primitive Carnivora, so abundantly represented in the Eocene deposits both of America and Europe, to which Cope has given the name of Creodonta. The Carnivora also appear to have been closely connected with the primitive Ungulates as represented by the extinct group called Condylarthra. In another direction the step from the Insectivores to the Lemurs is not great, and in past times the transition was probably complete. The Bats or Chiroptera are allied to the Insectivora in all characters except the extraordinary modification of their anterior extremities into wings; but this, like the want of the hind limbs in the Cetacea and Sirenia, makes such a clear distinction between them and all other mammals that, in the absence of any knowledge of any completely intermediate or transitional forms, they can be perfectly separated, and constitute as well-defined an order as any in the class. We have, however, an inkling of the mode in which the Insectivora were modified into Chiroptera shown us by the so-called Flying Lemur (_Galeopithecus_). Finally, we have the important and well-characterised group called Primates, including all the Monkeys and Man; and the question is not yet solved as to how and through what forms this is linked on to the other groups. It is commonly assumed that the Lemurs are nothing more than inferior Primates, but the interval between them in the actual fauna of the world is very great, and our knowledge of numerous extinct types recently discovered in America, said to be intermediate in characters, is not yet sufficient to enable us to form a definite opinion upon the subject.

The Edentata may be taken first as standing in some respects apart from all the others; and the Primates must be placed at the head of the series. The position of the others is quite arbitrary, as none of the hitherto proposed associations of the orders into larger groups stand the test of critical investigation, and palæontological researches have already gone far to show that they are all modifications of a common heterodont, diphyodont, pentadactylate form.

_Order_ EDENTATA.

The name assigned to this group (which some zoologists think ought rather to be ranked as a subclass[88] than an order) by Cuvier is often objected to as inappropriate—for although some of the members are edentulous, others have very numerous teeth—and the Linnæan name Bruta is occasionally substituted. But that term is quite as objectionable, especially since the group to which Linnæus applied it is by no means equivalent to the order as now understood, as the names of the genera contained in it, viz. _Elephas_, _Trichechus_, _Bradypus_, _Myrmecophaga_, _Manis_ and _Dasypus_, indicate. It contained, in fact, all the animals then known which are comprised in the modern groups of Proboscidea, Sirenia and Edentata together with the Walrus, one of the Carnivora. If retained at all, it should rather belong to the Proboscidea, as _Elephas_ stands first in the list of genera in the _Systema Naturæ_. Cuvier’s order included the _Ornithorhynchus_ and _Echidna_, the structure of which was then imperfectly known, and which are now by common consent removed to an altogether different section of the class; but otherwise its limits are those now adopted. The name Edentata is so generally used, and its meaning so well understood, that it would be undesirable to change it now; in fact similar reasons might be assigned for ceasing to use nearly all the other current ordinal designations, for it might be equally well objected that all Carnivora are not flesheaters, many of the Marsupialia have not pouches, and so forth.

If the teeth are not always absent, they invariably exhibit certain imperfections, which are indeed almost the only common characters binding together the various extinct and existing members of the order. These are—that they are homodont and, with the remarkable exceptions of _Tatusia_ and _Orycteropus_, monophyodont; they are never rooted, but have persistent pulps; except in some fossil forms, they are always deficient in one of the constituents which enter into the formation of the complete mammalian tooth, the enamel; and, at least among living forms, are never present either in the upper or lower jaw in the fore part of the mouth, the situation occupied by the incisors of other mammals.[89]

The peculiar nature of the dentition in the aberrant _Orycteropus_ will be noticed under the heading of that genus. As a rule, the coracoid process of the scapula of the Edentates is more developed than in other Eutheria.

The degree of development of the brain varies considerably in the different families, the hemispheres being in some cases almost or quite smooth (Fig. 57), with a small corpus callosum, and large anterior commissure; while in other instances the hemispheres are convoluted, and the corpus callosum is larger.

[Illustration: FIG. 57.—Upper surface of the brain of the Broad-banded Armadillo (_Xenurus unicinctus_). The large olfactory lobes are seen at the anterior extremity (left of figure); the hemispheres have only three sulci. (From Garrod, _Proc. Zool. Soc._ 1878, p. 230).]

There is so great a difference in structure and habits between some of the existing animals assigned to this order that, beyond the negative characters just mentioned, there seems little to connect them. The Sloths and Anteaters, for instance, in mode of life, general conformation of limbs, structure of digestive organs, etc., appear at first sight almost as widely separated as any mammals. Palæontology has, however, thrown great light upon their relations, and proved their real affinities. Perfectly intermediate forms have been discovered in the great Ground Sloths of America, which have the dentition and general form of the head of the Sloths, combined with the limbs and trunk of the Anteaters. It is, indeed, highly probable that the existing members of this order are very much differentiated representatives of a large group, the greater number of which are now extinct, and have become so without ever attaining a high grade of organisation. The great diversity of structure in the existing families, the high degree of specialisation to which many have attained, the paucity of species and even of individuals, their limited area of distribution, and their small size compared with known ancestral forms, all show that this is an ancient and a waning group, the members of which seem still to hold their own either by the remoteness and seclusion of their dwelling-places, by their remarkable adaptation of structure to special conditions of life, or by aid of the peculiar defensive armature with which they are invested. Their former history can, however, only be thus surmised, rather than read, at present; for, though we have ample evidence of the abundance and superior magnitude of certain forms in the most recent or Pleistocene geological age, yet we have at present no definite evidence as to their origin, or relationship to other orders of mammals.

The existing members of the order readily group themselves into five distinct families, the limits of which are perfectly clear. These are (1) _Bradypodidæ_, or Sloths; (2) _Myrmecophagidæ_, or Anteaters; (3) _Dasypodidæ_, or Armadillos; (4) _Manidæ_, Pangolins or Scaly Anteaters; and (5) _Orycteropodidæ_, Aard-varks or African Anteaters. The geographical distribution of these families coincides with their structural distinction, the first three being inhabitants of the New and the last two of the Old World. It has been usual to arrange these families into two large groups or suborders: (1) the Phyllophaga, leaf-eaters, also called Tardigrada, containing the _Bradypodidæ_ alone; and (2) the Entomophaga, insect-eaters, or Vermilingua, containing all the other families, from which sometimes the _Orycteropodidæ_ are separated as a third suborder under the name of Effodientia, or Tubulidentata. Such an arrangement is, however, an artificial one, founded on superficial resemblance. The bonds which unite the _Manidæ_ to the _Myrmecophagidæ_ are mainly to be found in the structure of the mouth, especially the extensile character of the tongue, the great development of the submaxillary glands, and the absence of teeth. These characters are exactly analogous to those found in the Echidna among Monotremes, the Woodpeckers among Birds, and the Chameleon among Reptiles,—the fact probably being that in countries where Termites and similar insects flourish various distinct forms of vertebrates have become modified in special relation to this abundance of nutritious food, which could only be made available by a peculiar structure of the alimentary organs. A close study of the more essential portions of the anatomy of these animals[90] leads to the belief that all the American Edentates at present known, however diversified in form and habits, belong to a common stock. Thus the _Bradypodidæ_, _Megatheriidæ_, and _Myrmecophagidæ_ are certainly allied, the modifications seen in the existing families relating only to food and manner of life. The ancestral forms may have been omnivorous, and gradually separated into the purely vegetable and purely animal feeders; from the former are developed the modern Sloths, from the latter the Anteaters. The Armadillos (_Dasypodidæ_) are another modification of the same type, retaining some generalised characters, as those of the alimentary organs, but in other respects, as in their defensive armature, remarkably specialised. The two Old World families _Manidæ_ and _Orycteropodidæ_ are so essentially distinct, both from the American families and from each other, that it may even be considered doubtful whether they are derived from the same primary branch of mammals, or whether they may not be offsets of some other branch, the remaining members of which have been lost to knowledge. Further remarks on this point are recorded under the description of the _Orycteropodidæ_.[91]

_Family_ BRADYPODIDÆ.

Externally clothed with long, coarse, crisp hair. Head short and rounded. External ears inconspicuous. Teeth ⁵⁄₄ in each jaw, subcylindrical, of persistent growth, consisting of a central axis of vaso-dentine, with a thin investment of hard dentine, and a thick outer coating of cement; without (so far as is yet known) any succession. Clavicles present. Fore limbs greatly longer than the hind limbs. All the extremities terminating in narrow, curved feet; the digits never exceeding three in number, encased for nearly their whole length in a common integument, and armed with long strong claws. Tail rudimentary. Stomach complex. No cæcum. Uterus simple and globular. Placenta deciduate, dome-like, composed of an aggregation of numerous discoidal lobes. Strictly arboreal in habits, vegetable feeders, and limited geographically to the forest regions of South and Central America.

[Illustration: FIG. 58.—Two-toed Sloth (_Cholœpus hoffmanni_).]

The Sloths, as the animals of this family are called on account of the habitual sluggishness of their movements, are the most strictly arboreal of all mammals, living entirely among the branches of trees, usually hanging under them, with their backs downwards (Fig. 58), and clinging to them with the simple hook-like organs to which the terminations of all their limbs are reduced. When they are obliged from any cause to descend to the ground, which they rarely, if ever, do voluntarily, their limbs, owing to their unequal length and the peculiar conformation of the feet—which allows the animals to rest only on the outer edge—are most inefficient for terrestrial progression, and they crawl along a level surface with considerable difficulty. Though generally slow and inactive, even when in their natural haunts, Sloths can on occasions travel with considerable rapidity along the branches; and, as they do not leap, like most other arboreal creatures, they avail themselves of the swaying of the boughs by the wind to pass from tree to tree. They feed entirely on leaves and young shoots and fruits, which they gather in their mouth, the fore limbs aiding in dragging boughs within reach, but not being used like hands, as they are by monkeys, squirrels, etc. When sleeping they roll themselves up in a ball, and, owing to the dry shaggy character of their hair, are very inconspicuous among the mosses and lichens with which the trees of their native forests abound; the concealment thus afforded being heightened in some species by the peculiar greenish tint of the outer covering—very uncommon in mammals. This is not due to the colour of the hair itself, but to the presence upon its surface of an alga, the lodgment of which is facilitated by the fluted or rough surface of the exterior of the hair, and the growth of which is promoted by the dampness of the atmosphere in the gloomy tropical forests, as it soon disappears from the hair of animals kept in captivity in England. Sloths are nocturnal, silent, inoffensive, and solitary animals, and usually produce but one young at birth. They appear to show an almost reptilian tenacity of life, surviving the most severe injuries and large doses of poisons, and exhibiting longer persistence of irritability of muscular tissue after death than other mammals.

In the _Bradypodidæ_, as well as in the _Myrmecophagidæ_, the testes are placed close to each other, lying on the rectum between it and the bladder; the penis is quite rudimentary, consisting of a pair of small corpora cavernosa, not directly attached by their crura to the rami of the ischia, and having a glans scarcely larger than that of the clitoris of most mammals, and, as in birds and reptiles, without any true corpus spongiosum. In the females of both families the uterus is simple and globular; and the vagina, at least in the virgin state, is divided into two channels by a strong median partition. The deciduate placenta of _Cholœpus_ is composed of a number of lobes aggregated into a dome-like mass; and it does not appear that the placenta of the Anteaters departs in any important characters from this type. According to the late Professor W. K. Parker, the embryos of the Sloths, Anteaters, and Pangolins have the stapes of the middle ear in the form of a rod, thus showing affinities with a very primitive type of mammalian organisation.

The Sloths were all included in the Linnæan genus _Bradypus_, but Illiger very properly separated the species with but two claws on the fore feet, under the name of _Cholœpus_, leaving _Bradypus_ for those with three.

_Bradypus._[92]—Three-toed Sloths. Teeth usually ⁵⁄₄ on each side; no tooth projecting greatly beyond the others; the first in the upper jaw much smaller than any of the rest; the first in the lower jaw broad and compressed; the grinding surfaces of all much cupped. Vertebræ: C 9, D and L 20 (of which 15 to 17 bear ribs), S 6, C 11. All the known species present the remarkable peculiarity of possessing nine cervical vertebræ, _i.e._ nine vertebræ in front of the one which bears the first thoracic rib (or first rib connected with the sternum, and corresponding in its general relations with the first rib of other mammals); but the ninth, and sometimes the eighth, bears a pair of short movable ribs. The arms or fore limbs are considerably longer than the hind legs. The bones of the fore arm are complete, free, and capable of pronation and supination. The hand is long, very narrow, habitually curved, and terminates in three pointed curved claws, in close apposition with each other. The claws are, in fact, incapable of being divaricated, so that the hand is reduced to the condition of a triple hook, fit only for the function of suspension from the boughs of trees. The foot closely resembles the hand in its general structure and mode of use; the sole being habitually turned inwards, so that it cannot be applied to the ground in walking. The tongue is short and soft, and the stomach large and complex, bearing some resemblance to that of the ruminating Ungulates. The windpipe or trachea has the remarkable peculiarity among mammals—not unfrequent among birds and reptiles—of being folded on itself before it reaches the lungs. The mammæ are two, and pectoral in position.

“Ai” is the common name given in books to the Three-toed Sloths. They were all comprised by Linnæus under the species _Bradypus tridactylus_. More recently Dr. Gray described as many as eleven species, ranged in two genera, _Bradypus_ and _Arctopithecus_; but the distinctions which he assigned both to species and genera do not bear close examination. Some are covered uniformly with a gray or grayish-brown coat; others have a dark collar of elongated hairs around the shoulders (_B. torquatus_); some have the hair of the face very much shorter than that of the rest of the head and neck; and others have a remarkable-looking patch of soft short hair on the back between the shoulders, consisting, when best marked, of a median stripe of glossy black, bordered on each side by bright orange, yellow, or white. There are also structural differences in the skulls, as in the amount of inflation of the pterygoid bones, which indicate real differences of species; but the materials in our museums are not yet sufficient to correlate these with external characters and geographical distribution. The habits of all are apparently alike. They are natives of Guiana, Brazil, and Peru, and one if not two species (_B. infuscatus_ and _B. castaneiceps_) extend north of the Isthmus of Panama as far as Nicaragua. Of the former of these Dr. Seeman says that, though generally silent, a specimen in captivity uttered a shrill sound like a monkey when forcibly pulled away from the tree to which it was holding.

_Cholœpus._[93]—Teeth ⁵⁄₄; the most anterior in both jaws separated by an interval from the others, very large, caniniform, wearing to a sharp, bevelled edge against the opposing tooth, the upper shutting in front of the lower when the mouth is closed (Fig. 59), unlike the true canines of heterodont mammals. Vertebræ: C 6 or 7, D 23-24, L 3, S 7-8, C 4-6. One species (_C. didactylus_) has the ordinary number of vertebræ in the neck; but an otherwise closely allied form (_C. hoffmanni_) has but six. The tail is very rudimentary. The hand generally resembles that of _Bradypus_; but there are only two functional digits with claws—those answering to the second and third of the typical pentadactylate manus. The structure of the hind limb generally resembles that of _Bradypus_, the appellation “two-toed” referring only to the anterior limb, for in the foot the three middle toes are functionally developed and of nearly equal size. _C. didactylus_, which has been longest known, is commonly called by the native name of _Unau_. It inhabits the forests of Brazil. _C. hoffmanni_ (Fig. 58) has a more northern geographical range, extending from Ecuador through Panama to Costa Rica. Its voice, which is seldom heard, is like the bleat of a sheep, and if the animal is seized it snorts violently. Both species are very variable in external coloration.

[Illustration: FIG. 59.—Skull of Two-toed Sloth (_Cholœpus didactylus_). From _Proc. Zool. Soc._ 1871, p. 432.]

_Nothropus._[94]—The only fossil form which has been referred to this family is indicated by a lower jaw, described by Dr. Burmeister, from the Pleistocene of Argentina, which appears to have belonged to an animal of about double the dimensions of _Cholœpus didactylus_. Professor Cope states, however, that this jaw really belongs to a Glyptodont; while it is referred by Dr. Ameghino to the next family.

_Family_ MEGATHERIIDÆ.

[Illustration: FIG. 60.—Section of upper molar teeth of _Megatherium americanum_. × ⅓. _p_, pulp-cavity; the other letters explained in the text. (After Owen.)]

The members of this family are all extinct. Their characters, so far as is known from the well-preserved remains of many species found abundantly in deposits of Pleistocene age in both North and South America, were intermediate between those of the existing _Bradypodidæ_ and the _Myrmecophagidæ_, combining the head and dentition of the former with the structure of the vertebral column, limbs, and tail of the latter. Almost all the known species are of comparatively gigantic size, the smallest, _Nothrotherium escrivanense_, exceeding the largest existing Anteater, and the Megatherium being larger than a Rhinoceros. The femur has no third trochanter, and the odontoid process of the axis vertebra has a peculiar facet on the ventral surface. The dentition is usually ⁵⁄₄ on each side, as in the Sloths, but ⁴⁄₃ in _Nothrotherium_.[95] This genus, and in a still more marked degree _Megatherium_, differ from all the others in the details of the structure of the teeth. They are very deeply implanted, of prismatic form (quadrate in transverse section), and the component tissues—hard dentine (Fig. 60, _d_), softer vaso-dentine (_v_), and cement (_c_)—are so arranged that, as the tooth wears, the surface always presents a pair of transverse ridges, thus producing a triturating apparatus comparable to the “bilophodont” molar of _Dinotherium_, _Tapirus_, _Manatus_, _Macropus_, and others, though produced in a different manner. In all the other genera the teeth are more or less cylindrical, though sometimes laterally compressed or even longitudinally grooved on the sides, and on the grinding surface the prominent ridge of hard dentine follows the external contour, and is surrounded only by a thin layer of cement, as in the existing Sloths. The Ground Sloths, as the members of this family may be conveniently designated, agree with the Sloths and Anteaters, and thereby differ from all other mammals, in that the coracoid process of the scapula and the coracoidal border of the same unite over the coraco-scapular notch, which is thus converted into a foramen. Large clavicles are present.

_Megatherium._[96]—The typical genus _Megatherium_, as being the longest known representative of the family, may be noticed in some detail. A nearly complete skeleton, found on the banks of the River Luxan, near Buenos Ayres, and sent in 1789 to the Royal Museum at Madrid, long remained the principal if not the only source of information with regard to the species to which it belonged, and furnished the materials for many descriptions, notably that of Cuvier, who determined its affinities with the Sloths.[97] In 1832 an important collection of bones of the Megatherium was discovered near the Rio Salado, and secured for the Museum of the College of Surgeons of England; and these, with another collection found at Luxan in 1837, and now in the British Museum, supplied the materials for the complete description of the skeleton published by Sir R. Owen in 1861. Other skeletons have subsequently been received by several of the Continental museums, as Milan and Paris, and also by those in South America; and consequently our knowledge of the organisation of the Megatherium, so far as it can be deduced from the bones and teeth, is as complete as that of any other animal, recent or extinct.

[Illustration: FIG. 61.—Oral surface of mandible of _Megatherium americanum_. _a_, Condyle; _b_, masseteric process; _c_, angle; _d_, symphysis. (After Owen.)]

The remains hitherto spoken of are all referred to one species, _Megatherium americanum_ of Blumenbach (_M. cuvieri_ of Desmarest), and are all from the newest or Pleistocene geological formations of the Argentine Republic and Paraguay, or the lands forming the basin of the Rio de la Plata. Dr. Leidy has described, from similar formations in Georgia and South Carolina, bones of a closely allied species, about one-fourth smaller, which he has named _M. mirabile_. Three other South American species have been described; but _M. laurillardi_, of Lund, founded upon remains found in Brazil, has been made the type of the genus _Ocnopus_.

[Illustration: FIG. 62.—Skeleton of _Megatherium_, from the specimen in the Museum of the Royal College of Surgeons. × ¹⁄₂₅.]

The following description will apply especially to the best-known South American form, _Megatherium americanum_. In size it exceeded any existing land animal except the elephant, to which it was inferior only in consequence of the comparative shortness of its limbs; for in length and bulk of body it was its equal, if not superior. The full length of a mounted skeleton (Fig. 62), from the fore part of the head to the end of the tail, is 18 feet, of which the tail occupies 5 feet. The head, which is small for the size of the animal, presents a general resemblance to that of the Sloth; the anterior part of the mouth is, however, more elongated, and the jugal bone, though branched posteriorly in the same way as that of the Sloth, meets the zygomatic process of the squamosal, thus completing the arch. The lower jaw has the middle part of its horizontal ramus curiously deepened, so as to admit of implantation of the very long-rooted teeth, the peculiar structure of which has been already described. A skull recently discovered shows that, instead of the wide gap between the extremity of the nasals and the premaxillæ exhibited in Fig. 62, there was a prenasal bone, towards which a process extended upwards and backwards from the extremity of the upper surface of the premaxillæ.

The vertebral column consists of seven cervical, sixteen dorsal, three lumbar, five sacral, and eighteen caudal vertebræ. The spinous processes are much better developed than in the Sloths, and are all directed backwards, there being no reversing of the inclination near the posterior end of the dorsal series, as in most active-bodied mammals. In the lumbar region, the accessory zygapophyses, rudimentary in Sloths, are fully developed, as in the Anteaters.

The tail is large, and its basal vertebræ have strong lateral and spinous processes and chevron bones, indicating great muscular development. The scapula resembles that of the Sloths in the union of the acromion with the coracoid, and in the bridging over of the suprascapular notch. The clavicle is complete and very large, much resembling that of man on a large scale. The fore limbs are longer than the hind limbs. The humerus has no entepicondylar foramen. The radius and ulna are both well developed, and have a considerable amount of freedom of movement. The hand is singularly modified. The pollex is represented only by a rudimentary metacarpal, but the next three digits are large, and terminate in phalanges adapted for the support of immense claws, the middle one being especially large. The outer or fifth digit has no claw, and it may be considered as certain that the weight of the foot was, in standing and walking, chiefly thrown upon this one, which was protected by a callous pad below, as in the existing great Anteater, while the other toes were curved inwards towards the palm, and only came in contact with the ground by their outer surfaces. The mechanical arrangements by which the weight of the body was thrown entirely upon the outer side of the foot are very curious, and are fully described in Owen’s memoir. The pelvis is remarkably wide, even more so than that of the Elephant, but it is formed on the same principle as in the Sloths. The femur is extremely broad and flattened; the tibia and fibula are short and strong, and united together at each end. The hind foot, contrary to the usual rule in the Edentata, is even more singularly modified than the hand. Thus the ankle-joint is formed upon a peculiar plan, quite unlike that of the Sloths, or of any other mammal, except the Megatherium’s nearest allies; and the calcaneum projects nearly as far backwards as the fore part of the foot does forwards. There is no trace of great toe or hallux, or of its corresponding cuneiform bone; the second toe is rudimentary; while the third has an enormous ungual phalanx, which, as in those of the hand, is remarkable for the immense development of the bony sheath reflected from its proximal end around the base of the claw. The two outer toes have large and very peculiarly-shaped metatarsals, but only small phalanges, and no claws. The creature probably walked upon the outer edge of the sole, so that the great falcate claw of the third toe did not come into contact with the ground, and so was kept in a state of sharpness ready for use. The foot was therefore formed upon quite a different principle from that of the Anteaters or Sloths, though somewhat like the latter in having two of the toes aborted.

Taking all the various points of its structure together, they clearly indicate affinities both with the existing Sloths and with the Anteaters, the skull and teeth more resembling those of the former, and the vertebral column and limbs the latter. It is also not difficult to infer the food and habits of this enormous creature. That it was a leaf-eater there can be little doubt; but the greater size and more complex structure of its teeth might have enabled it to crush the smaller branches as well as the leaves and succulent shoots which form the food of the existing Sloths. It is, however, very improbable that it climbed into the branches of the trees like its diminutive congeners, and it is far more likely that it obtained its subsistence by tearing them down with the great hook-like claws of its powerful prehensile fore limbs, being easily enabled to reach them by raising itself up upon the massive tripod formed by the two hind feet, firmly fixed to the ground by the one huge falcate claw, and the stout, muscular tail. The whole conformation of the hinder part of the animal is strongly suggestive of such an action. There can also be little doubt but that all its movements were as slow and deliberate as those of its modern representatives.

An idea at one time prevailed that the Megatherium was covered externally with a coat of bony armour like that of the Armadillos; but this originated in dermal plates belonging to the Glyptodon having been accidentally associated with bones of the Megatherium. Similar plates, on a smaller scale, have indeed been found in connection with the skeleton of the Mylodon, but never yet with the Megatherium, which we may therefore imagine with a covering of coarse hair like that of its nearest living allies, the Sloths and Anteaters.

_Scelidotherium_, _Mylodon_, etc.—Of the more important remaining genera of this family a briefer notice will suffice. _Scelidotherium_ (in which _Platyonyx_ may be included) comprises several species of considerably smaller dimensions than the Megatherium, and is in some respects intermediate between that genus and _Mylodon_. The teeth have an oval cross-section, like those of the Sloths, while the skull, in which the length of the nasals is subject to great variation in the different species, approximates more or less closely to that of the _Myrmecophagidæ_. The humerus generally has an entepicondylar foramen; and the form and relations of the bones of the feet differ considerably from those obtaining in the type genus. _S. leptocephalum_, the type of the genus, occurs in Patagonia and Argentina but other species are found in Brazil and Chili. The genus _Mylodon_, in its widest sense, may be taken to include a number of comparatively large Edentates, some of which have been described under the names of _Grypotherium_, _Lestodon_, and _Pseudolestodon_. The teeth of the upper jaw are generally of an oval or subtriangular section; and in the more typical forms the first and second teeth are separated by a short interval, the former being horizontally worn. In other species, however, like _M. (Lestodon) armatus_, there is a considerable space between the first and second teeth, and the first is worn obliquely. The skull is exceedingly like that of the Sloths in general contour; and there is not the descending process at the angle of the mandible found in _Megatherium_. The humerus has no entepicondylar foramen. The species represented in Fig. 63 is from the Pleistocene of South America; but the type of the genus is _M. harlani_, from beds of corresponding age in Kentucky. The Patagonian _M. (Grypotherium) darwini_ is a remarkable form, characterised by the presence of a bony arch connecting the premaxillæ with the nasals, of which, as already mentioned, there is an incomplete development in _Megatherium_. _Megalonyx_, from the Pleistocene of Kentucky, differs from _Mylodon_ by the long interval between the first and second teeth, and also by the presence of an entepicondylar foramen in the humerus. _Nothrotherium_ is a smaller form, occurring in the deposits of the Brazilian caves, of which the dental features have been already mentioned. The osteological characters of these and other allied genera have been fully described in the works of Cuvier, Owen, Burmeister, Leidy, Ameghino, Gervais, Reinhardt, and others.

[Illustration: FIG. 63.—Skeleton of _Mylodon robustus_ (Pleistocene, South America). From Owen.]

_Promegatherium._—Two genera from the infra-Pampean beds of Argentina, described as _Promegatherium_ and _Promylodon_, are respectively distinguished from _Megatherium_ and _Mylodon_ by the presence of bands of enamel on the teeth, which points to the descent of the Edentates from mammals with enamelled teeth.

The Tertiary North American forms described as _Moropus_ and _Morotherium_,[98] and originally regarded as Edentates, would appear to be aberrant Ungulates.

_Family_ MYRMECOPHAGIDÆ.

Externally clothed with hair. No teeth. Head elongated. Mouth tubular, with a small terminal aperture, through which the long, vermiform tongue, covered with the viscid secretion of the enormous submaxillary glands, is rapidly protruded in feeding, and withdrawn again with the adhering particles of aliment, which are then sucked into the pharynx. Clavicles rudimentary. In the manus, the third toe is greatly developed, and has a long falcate claw, the others are reduced or suppressed. The pes has four or five subequal digits with claws. Posterior dorsal and lumbar vertebræ, with additional interlocking zygapophyses. Tail long, sometimes prehensile. Uterus simple. Placenta dome-like or discoidal. Brain fairly convoluted, and with a large corpus callosum and anterior commissure. The animals of this family are the “Anteaters” _par excellence_. They feed exclusively on animal substances, mostly insects. One species is terrestrial, the others arboreal; none burrow in the ground. They are all inhabitants of the Neotropical region.

The reproductive organs, as noticed on p. 181, are of the same general type as in the _Bradypodidæ_.

_Myrmecophaga._[99]—Skull greatly elongated and narrow, its upper surface smooth and cylindriform. Anteriorly the face is produced into a long, tubular rostrum, rounded above and flattened below, with terminal nares, and composed of the mesethmoid ossified for more than half its length, the vomer, the maxillæ, and the long and narrow nasal bones, the premaxillæ being extremely short and confined to the margin of the anterior nares. The zygomatic arch is incomplete, the styliform jugal only articulating with the maxilla in front, and not reaching to the very short zygomatic process of the squamosal. The lachrymal foramen is in front of the margin of the orbit. There are no postorbital processes to the frontals, or any other demarcation between the orbits and the temporal fossæ. Palate extremely elongated, and produced backwards as far as the level of the external auditory meatus by the meeting in the middle line of the largely developed pterygoids. The glenoid fossa a shallow oval facet, with its long diameter from before backwards. Mandible very long and slender with an exceedingly short symphysis, no distinct coronoid process, and a slightly elevated, elongated, flattened, condylar articular surface. Vertebræ: C 7, D 15-16, L 3-2, S 6, C 31. Clavicles rudimentary. In the manus the first digit is very slender, the second also slender, with compressed phalanges of nearly equal length. The third digit is immensely developed; though its proximal phalanx is extremely short, its ungual phalanx is so long that the entire length of the digit exceeds that of the second. The fourth has a long and rather slender metacarpal, and three phalanges diminishing in size, the ungual phalanx being very small. The fifth has the metacarpal nearly as long, but not so stout, as the fourth, and followed by two small phalanges, the last rudimentary and conical. Claws are developed upon all but the fifth. In walking the toes are kept strongly flexed, and have their points turned upwards and inwards, the weight being supported upon a callous pad over the end of the fifth digit, and by the dorsal surfaces of the third and fourth digits. The hind feet are short and rather broad, with five subequal claws, the fourth the longest, the first shortest; the whole sole is placed on the ground in walking. Body rather compressed, clothed with long, coarse hair. Tail about as long as the body, and covered with very long hair; not prehensile. Ears small, oval, erect. Eyes very small. Stomach consisting of a subglobular, thin-walled, cardiac portion, and a muscular pyloric gizzard with dense epithelial lining. No ileo-colic valve, and a short wide ill-defined cæcum. Mammæ two, pectoral.

There is one species,[100] _M. jubata_, the Great Anteater, or Ant Bear (Fig. 64), measuring 4 feet in length without the tail, and upwards of 2 feet in height at the shoulder. Its prevailing colour is gray, with a broad black band, bordered with white, commencing on the chest, and passing obliquely over the shoulder, diminishing gradually in breadth as it approaches the loins, where it ends in a point. It is extensively distributed in the tropical parts of South and Central America, frequenting low swampy savannas along the banks of rivers, and the depths of the humid forests, but is nowhere abundant. Its food consists mainly of termites, to obtain which it opens their nests with its powerful sharp anterior claws, and as the insects swarm to the damaged part of their dwelling, it draws them into its mouth by means of its long, flexible, rapidly-moving tongue covered with glutinous saliva. The Great Anteater is quite terrestrial in its habits, being never known to climb trees, nor does it burrow underground like the Armadillos. Though generally an inoffensive animal, when attacked it can defend itself vigorously and effectively with its sabre-like anterior claws. The female bears but a single young at a birth.

The union of the pterygoids in the middle line to prolong the narial passage is a character found elsewhere among existing mammals only in the next genus, in one Armadillo (_Tatusia_), and in certain Cetacea. The contrast in length between the skull of the Great Anteater and that of the Sloth is, as Professor Parker observes, very marked indeed; the one being relatively the longest and the other almost the shortest in the whole class. The small size and incomplete development of the jugal bone in the zygomatic arch affords another striking contrast to the Sloths (Fig. 59).

[Illustration: FIG. 64.—The Great Anteater (_Myrmecophaga jubata_). (From Sclater, _List of Animals in Zoological Society’s Gardens_, 1883, p. 190.)]

_Tamandua._[101]—This genus closely resembles the last in anatomical structure, but the head is much less elongated, the fur is short and bristly, the tail tapering, prehensile, with the under side throughout and the whole of the terminal portion naked and scaly. The stomach is similar to that of _Myrmecophaga_, but with the muscular pyloric gizzard not quite so strongly developed. There is a distinct ileo-colic valve and a short globular cæcum. The fore foot has a very large claw on the third toe, moderate-sized claws on the second and fourth, a very minute one on the first, and none on the fifth, which is entirely concealed within the skin. The hind foot has five subequal claws. Vertebræ: C 7, D 17, L 2, S 5, C 37. There are very rudimentary clavicles.

[Illustration: FIG. 65.—Tamandua Anteater (_Tamandua tetradactyla_). From _Proc. Zool. Soc._ 1871, pl. xliii.]

The Tamandua (Fig. 65) is much smaller than the Great Anteater, and differs essentially from it in its habits, being mainly arboreal. It is an inhabitant of the dense primeval forests of South and Central America. As different individuals vary much in their coloration, it is possible that there may be more than one species. The usual colour is yellowish-white, with a broad black lateral band, covering nearly the whole of the side of the body.

[Illustration: FIG. 66.—Cæca of the Two-toed Anteater (_Cycloturus didactylus_). _i_, Ileum; _c_, colon.]

_Cycloturus._[102]—The skull is much shorter even than in _Tamandua_, and is arched considerably in the longitudinal direction. It differs from that of the other members of the family mainly in the long canal for the posterior nares not being closed by bone below, as the greater part of the palatines and the pterygoids do not meet in the middle line. The mandible has a prominent, narrow, recurved coronoid, and a well-developed angular process; it is strongly decurved in front. Vertebræ: C 7, D 16, L 2, S 4, C 40. Ribs remarkably broad and flat. Clavicles well developed. Manus remarkably modified, the third digit being greatly developed at the expense of all the others, and having a stout short metacarpal and but two phalanges, of which the most distal is large, compressed, pointed, and much curved, and bears a very strong hook-like claw. The second digit has the same number of phalanges, and bears a claw, but is very much more slender than the third. The fourth is represented only by the metacarpal and one nailless phalanx, the first and fifth only by very rudimentary metacarpals. The pes is also completely modified into a climbing organ. The hallux is rudimentary, consisting of a metatarsal and one phalanx, concealed beneath the skin; but the other four toes are subequal and much curved, with long pointed compressed claws. The tuber calcanei is directed towards the plantar surface, and parallel with it and extending to about double its length is a greatly elongated sesamoid ossicle. These together support a prominent calcarine cushion, to which the nails are opposed in climbing. Stomach pyriform, with muscular walls, but no distinct gizzard-like portion, as in the foregoing genera. Commencement of the colon provided with two small cæca (Fig. 66), resembling those of many birds, narrow at the base, and rather dilated at their terminal blind ends, and communicating with the general cavity by very minute apertures. Tail longer than the body, tapering, bare on the under surface, and very prehensile. Fur soft and silky.

This genus has also but one species certainly known, the Little or Two-toed Anteater (_C. didactylus_), an animal not larger than a Rat, of a general yellowish-colour, and exclusively arboreal in its habits. It is a native of the hottest parts of South and Central America.

_Family_ DASYPODIDÆ.

The greater part of the skin strongly ossified. On the back and sides the union of numerous quadrate or polygonal scutes forms a hard shield, usually consisting of an anterior (scapular) and posterior (pelvic) solid portion (which overhang on each side the parts of the body they respectively cover, forming chambers into which the limbs are withdrawn), and a variable number of rings between, connected by soft flexible skin so as to allow of curvature of the body. The top of the head has also a similar shield (cephalic), and the tail is usually encased in bony rings or plates. The outer or exposed surfaces of the limbs are protected by irregular bony scutes, not united at their margins; but the skin of the inner surface of the limbs and under side of the body is soft, and more or less clothed with hair. Hairs also in many species project through apertures between the bony scutes of the back. The ossified dermal scutes are everywhere covered by a layer of horny epidermis. Teeth numerous, simple, of persistent growth, and usually monophyodont, but in one genus (_Tatusia_) a succession of teeth has been observed. Zygomatic arch of skull complete. Cervical vertebræ with extremely short, broad, and depressed bodies. The atlas free, but the second and third, and often several of the others, ankylosed together both by their bodies and arches. Lumbar vertebræ with accessory zygomatic processes, and very large metapophyses, supporting the bony carapace. Clavicles well developed. A third trochanter on the femur. Tibia and fibula ankylosed at their distal extremities. Fore feet with strongly developed, curved claws, adapted for digging and scratching—three, four, or five in number. Hind feet plantigrade, with five toes, all provided with nails. Tongue long, pointed, and extensile, though to a less degree than in the Anteaters. Submaxillary glands largely developed. Stomach simple. Uterus simple. Placenta discoidal, deciduate. The brain is generally characterised by the large size of the olfactory lobes (Fig. 57), and the slight development of sulci on the hemispheres; the sylvian fissure being represented only by a very open and shallow angle. From the earliest stage of development the stapes is stirrup-shaped, thus showing a nearer affinity to the higher mammals than is presented by the Sloths.

The animals of this family are commonly called Armadillos, a word of Spanish origin, having reference to their armour-like covering. The existing species are all of small or moderate size. They are mostly, though not universally, nocturnal in their habits, and are all omnivorous, feeding on roots, insects, worms, reptiles, and carrion. Armadillos are harmless and inoffensive creatures, offering no resistance when caught, their principal means of escape from their enemies being the extraordinary rapidity with which they can burrow in the ground, and the tenacity with which they retain their hold in their subterranean retreats. Notwithstanding the shortness of their limbs they can run with great rapidity. Most of the species are esteemed good eating by the natives of the countries in which they live. They are all inhabitants of the open plains or the forests of the tropical and temperate parts of South America, with the exception of one species (_Tatusia novemcincta_), which ranges as far north as Texas. Of the existing genera, _Chlamydophorus_ stands apart from the rest in the formation of its external covering; but in all other respects _Tatusia_ is the most aberrant form, exhibiting a peculiar type of structure of the fore feet, which in all the others show modifications, though in very varying degrees, of a single and different type.

The reproductive organs of the _Dasypodidæ_ differ from those of the Sloths and Armadillos in the presence of a largely developed copulating organ in the male, and of a simple vagina of corresponding length in the female. The testes are still abdominal, although not in the same position; and the penis still wants both the glans and bulb. The uterus is nearly or quite as simple as in the Sloths and Anteaters; and there is no reason to believe that the placentation is essentially different from that obtaining in the other groups.

Subfamily =Chlamydophorinæ=.—In most anatomical characters, especially the structure of the fore foot, this little group resembles the _Dasypodinæ_; but it differs remarkably from all other known Armadillos, living or extinct, in the peculiar modification of the dermal armour.

_Chlamydophorus._[103]—Teeth ⁸⁄₈₋₉, subcylindrical, somewhat compressed, moderate in size, smaller at each end (especially in front) than at the middle of the series. Skull broad and rounded behind, pointed in front. Muzzle subcylindrical and depressed. A conspicuous rounded, rough prominence on the frontal bone, just before each orbit. Tympanic prolonged into a tubular auditory meatus, curving upwards round the base of the zygoma. Vertebræ: C 7, D 11, L 3, S 10, C 15. Upper part of head and trunk covered with four-sided horny plates (with very small thin ossifications beneath), forming a shield, free, and overhanging the sides of the trunk, and attached only along the middle line of the back. The plates are arranged in a series of distinct transverse bands, about twenty in number between the occiput and the posterior truncated end, and not divided into solid thoracic and pelvic shields with movable bands between. The hinder end of the body is abruptly truncated and covered by a vertically-placed, strong, solid, bony shield, of an oval (transversely extended) form, covered by thin epidermic plates. This shield is firmly ankylosed by five bony processes to the hinder part of the pelvis. Through a notch in the middle of its lower border the tail passes out. The latter is rather short, cylindrical in its proximal half, and expanded and depressed or spatulate in its terminal portion, and covered with horny plates. The dorsal surfaces of the fore and hind feet are also covered with horny plates. The remainder of the limbs and under surface and sides of the body beneath the overlapping lateral parts of the dorsal shield are clothed with rather long, very soft, silky hair. Eyes and ears very small, and concealed by the hair. Extremities short. Feet large, each with five well-developed claws, those on the fore feet very long, stout, and subcompressed, the structure of the digits being essentially the same as those of _Xenurus_ and _Priodon_. Nipples two, pectoral. Visceral anatomy closely resembling that of _Dasypus_, the cæcum being broad, short, and bifid.

The Pichiciago (_C. truncatus_), a small burrowing animal, about 5 inches long, inhabits the sandy plains of the western part of the Argentine Republic, especially the vicinity of Mendoza. Its horny covering is of a pinkish colour, and its silky hair snow white. It is rare, and its habits are but little known. A second species, _C. retusa_, from Bolivia, has been described by Burmeister. It is of rather larger size, and has the dorsal shield attached to the skin of the back as far as its edge, instead of only along the median line.

Subfamily =Dasypodinæ=.—Fore feet usually with all five digits developed and with nails, though the first and fifth may be suppressed. The first and second long and slender, with the normal number and relative length of phalanges. The others stout, with short broad metacarpals, and the phalanges greatly reduced in length and generally in number by coalescence. The ungual phalanx of the third very large, that of the others gradually diminishing to the fifth. _Dasypus_, as now restricted, has the most normal form of manus, but the modifications so markedly developed in all the others (and culminating in _Tolypeutes_) are foreshadowed, as it were, in it. Ears wide apart. Mammæ one pair, pectoral.

_Dasypus._[104]—Teeth ⁹⁄₁₀ or ⁸⁄₉, of which the anterior in the upper jaw is usually implanted in the premaxillary bone. The series of teeth extends posteriorly some distance behind the anterior root of the zygoma, almost level with the hinder edge of the palate. They are large, subcylindrical, slightly compressed, diminishing in size towards each end of the series; the anterior two in the mandible much smaller, and more compressed than the others. Cranial portion of the skull broad and depressed. Facial portion triangular, broad in front and much depressed. Auditory bulla completely ossified, perforated on the inner side by the carotid canal, and continued externally into an elongated bony meatus auditorius, with its aperture directed upwards and backwards. (In all the remaining genera of _Dasypodinæ_ the tympanic bone is a mere half ring, loosely attached to the cranium.) Mandible with a high ascending ramus, broad transversely-placed condyle, and high slender coronoid process. Vertebræ: C 7, D 11-12, L 3, S 8, C 17-19. Head broad and flat above. Muzzle obtusely pointed. Ears of moderate size or rather small, placed laterally, far apart. Body broad and depressed. Carapace with six or seven movable bands between the scapular and pelvic shields, each plate, or scute, being marked by a regular ellipse formed of widely separated punctures. Tail shorter than the body, tapering, covered with plates forming distinct rings near the base. Fore feet with five toes; the first much more slender than the others, and with a smaller ungual phalanx and nail; the second, though the longest, also slender. The third, fourth, and fifth gradually diminishing in length, all armed with very strong, slightly curved, compressed claws, sloping away from an elevated rounded inner border to a sharp, outer, and inferior edge. The hind foot rather short, with all five toes armed with stout, compressed, slightly curved, obtusely pointed claws—the third the longest, the second nearly equal to it, the fourth the next, the first and fifth shorter, and nearly equal.

To this genus belongs one of the best known-species of the group, the Six-banded Armadillo or Encoubert (_D. sexcinctus_) of Brazil and Paraguay. A very similar species, _D. villosus_, the Hairy Armadillo, replaces it south of the Rio Plata. There are also two very small species—_D. vellerosus_, from the Argentine Republic and North Patagonia, and _D. minutus_ from La Plata. The latter differs from the other three in having no tooth implanted in the premaxillary bone. Remains apparently referable to _D. villosus_ occur in the Pleistocene cavern-deposits of Brazil.

_Xenurus._[105]—Teeth ⁹⁄₉ or ⁸⁄₈, of moderate size and subcylindrical. The most posterior placed a little way behind the anterior root of the zygoma, but far from the hinder margin of the palate. Cranium somewhat elongated, much constricted behind the orbits, and immediately in front of the constriction considerably dilated. Mandible slender; coronoid process very small and sharp-pointed, sometimes obsolete. Vertebræ: C 7, D 12-13, L 3, S 10, C 18. Head broad behind. Ears rather large and rounded, wide apart. Movable bands of carapace 12-13; the scutes being marked by an obscurely granular sculpture. Tail considerably shorter than the body, slender, and covered with nearly naked skin, with but a few small, scattered, dermal bony plates, chiefly on the under surface and near the apex. On the fore feet the first and second toes are long and slender, with small claws and the normal number of phalanges; the other toes have but two phalanges; the third has an immense falcate claw; the fourth and fifth similar but smaller claws. The hind feet are comparatively small, with five toes, bearing small, triangular, blunt nails; the third longest, the first shortest. The best known species of this genus, the Tatouay or Cabasson, _X. unicinctus_, is, after _Priodon gigas_, the largest of the group. It is found, though not abundantly, in Surinam, Brazil, and Paraguay, its remains occurring in the Pleistocene cavern-deposits of Brazil. Others, _X. hispidus_ and _lugubris_, have been described, but little is as yet known of them.

_Priodon._[106]—Teeth variable in number, and generally differing on the two sides of each jaw, usually from 20 to 25 on each side above and below, so that as many as 100 may be present altogether; but as life advances the anterior teeth fall out, and all traces of their alveoli disappear. The series extends as far back as the hinder edge of the anterior root of the zygoma. The teeth are all very small; those in the anterior half of each series being strongly compressed, with flat sides and a straight free edge; the posterior ones are more nearly cylindrical, with flat truncated, free surfaces. Vertebræ: C 7, D 12, L 3, S 10, C 23. Head small, elongated, conical. Ears moderate, ovate. Carapace with 12-13 movable bands. Tail nearly equal to the body in length, gradually tapering, closely covered with quadrangular scales, arranged in a quincunx pattern. Fore feet with five toes, formed on the same plan as those of _Xenurus_, but with the claw of the third of still greater size, and that of each of the others, especially the fifth, proportionately reduced. Hind foot short and rounded, with five very short toes, with short, broad, flat, obtuse nails. The only known species, the Great Armadillo (_P. gigas_), is by far the largest of existing members of the family, measuring rather more than 3 feet from the tip of the nose to the root of the tail, the tail being about 20 inches long. It inhabits the forests of Surinam and Brazil. The powerful falcate claws of its fore feet enable it to dig with great facility. Its food consists chiefly of termites and other insects, but it is said to attack and uproot newly-made graves for the purpose of devouring the flesh of the bodies contained in them.

_Tolypeutes._[107]—Teeth ⁹⁄₉ or ⁸⁄₉, rather large in proportion to the size of the skull, the hinder end of the series reaching nearly to the posterior margin of the palate. Vertebræ: C 7, D 11, L 3, S 12, C 13. Ears placed low on the sides of the head, rather large, broadly ovate. Carapace with its scapular and pelvic shields very free at the sides of the body, forming large chambers into which the limbs can be readily withdrawn. Only three movable bands; sculpture of scutes in the form of subconcentrically arranged granules. Tail short, conical, covered with large bony tubercles. The fore feet formed on the same type as in the last genus, but the peculiarities carried out to a still greater extent. The claw of the third toe is very long and falcate, the first and fifth greatly reduced and sometimes wanting. On the hind foot the three middle toes have broad, flat, subequal nails, forming together a kind of tripartite hoof; the first and fifth much shorter, with more compressed nails.

The Armadillos of this genus have the power of rolling themselves up into a perfect ball, the shield on the top of the head and the tuberculated dorsal surface of the tail exactly fitting into and filling up the apertures left by the notches at either end of the carapace. This appears to be their usual means of defence when frightened or surprised, as they do not burrow like the other species. They run very quickly, with a very peculiar gait, only the tips of the claws of the fore feet touching the ground. Three species are described:—_T. tricinctus_, the Apar; _T. conurus_, the Matico; and _T. muriei_. Remains apparently referable to _T. conurus_ are of not uncommon occurrence in the Brazilian cavern-deposits.

Subfamily =Tatusiinæ=.—This group contains but one genus, _Tatusia_.[108] Teeth ⁸⁄₈ or ⁷⁄₇, very small subcylindrical. The first and second subcompressed, the last considerably smaller than the others. They present the remarkable peculiarity (elsewhere found among Edentates, so far as is yet known, only in _Orycteropus_) of all being, with the exception of the last, preceded by two-rooted milk teeth, which are not changed until the animal has nearly attained its full size. Vertebræ: C 7, D 9-11, L 5, S 8, C 20-27. Head narrow, with a long, narrow, subcylindrical, obliquely-truncated snout; pterygoids meeting in the middle line below the nasal passage. Ears rather large, ovate, and erect, placed close together on the occiput. Carapace with seven to nine distinct movable bands; sculpture on scutes consisting of pits arranged in a V-shape. Body generally elongated and narrow. Tail moderate or long, gradually tapering; its dermal scutes forming very distinct rings for the greater part of its length. Fore feet with four visible toes, and a concealed clawless rudiment of the fifth. Claws all long, slightly curved, and very slender, the third and fourth subequal and alike, the first and fourth much shorter. Hind feet with five toes, all armed with strong, slightly curved, conical, obtusely-pointed nails. The third longest, then the second and fourth; the first and fifth much shorter than the others.

[Illustration: FIG. 67.—The Peba Armadillo (_Tatusia novemcincta_).]

This genus differs from all the other Armadillos in having a pair of inguinal mammæ, in addition to the usual pectoral pair, and in producing a large number (four to ten) of young at a birth, all the others having usually but one or two.

The Peba Armadillo, _T. novemcincta_ (Fig. 67), is a well-known species, having an extensive range from Texas to Paraguay. It is replaced in the more southern regions of South America by a smaller species, with shorter tail, the Mulita (_T. hybrida_), so called from the resemblance of its head and ears to those of a mule. _T. kappleri_ is a large species from Surinam.

A rare Armadillo from Peru described under the names of _Cryptophractus pilosus_ and _Praopus hirsutus_, but which evidently belongs to _Tatusia_, is of some interest owing to the thick coat of hair with which it is covered. This animal appears to be closely allied to _T. novemcincta_, from which it mainly differs by having the whole of the carapace covered with a thick coating of light brown, fine, but rather stiff hair, about an inch and a half in length. Similar hair is found on the cheeks, the proximal portions of the limbs, and (although less abundantly and shorter) on the under surface of the body. The cephalic shield, snout, feet, and the tail, with the exception of the root, are bare. The coating of hair on the back and sides completely conceals the carapace, except near the margin of the scapular region; but by separating the hairs the bands and scutes are rendered visible.[109]

In the Pleistocene cavern-deposits of Brazil have been found remains of _T. novemcincta_, and also of _T. punctata_, which appears to be an extinct form nearly allied to _T. kappleri_, but of somewhat larger size.

_Extinct genera._—In addition to remains referable to existing genera, the above-mentioned deposits have also yielded evidence of the former existence of extinct generic types of Armadillos, some of which attained very large dimensions. Of these _Eutatus_ was a large form distinguished from all existing genera by the circumstance that the whole of the carapace was composed of movable bands, which were thirty-three in number. _Dasypotherium_ was a still larger form, furnished with eight teeth, of which the second seems to have been larger than the others; this genus is regarded as connecting the modern Armadillos with the next one. The gigantic _Chlamydotherium_, the scutes of which are common in the Brazilian caves, is considered to have been as large as a Rhinoceros; the carapace has several movable bands, but the teeth approximate in structure to those of the next family, so that the genus tends to connect the Armadillos with the Glyptodonts.

_Family_ GLYPTODONTIDÆ.

[Illustration: FIG. 68.—Tooth of _Glyptodon_ from the side, and from the grinding surface. (After Owen.)]

In the Pleistocene cavern-deposits of Brazil, but still more abundantly in the fluviatile deposits which cover the country in the neighbourhood of Buenos Ayres, are found the remains of some of the most remarkable forms of mammals yet discovered, the Glyptodonts, which may be regarded as forming a separate extinct family. They differ from the existing _Dasypodidæ_ in their large size, and in having the carapace composed of a solid piece (formed by the union of a multitude of bony dermal scutes) without any movable rings, and in usually having also a ventral piece or plastron. The facial portion of the skull is very short. A long process of the maxillary bone descends from the anterior part of the zygomatic arch. The ascending ramus of the mandible is remarkably high. The teeth are ⁸⁄₈ in the known species, all much alike, having two deep grooves or flutings on each side, so as to divide them into three nearly distinct lobes (Fig. 68). The vertebral column is almost entirely ankylosed into a solid tube, and there is a complex joint at the base of the neck, to allow of the head being retracted within the carapace. The limbs are very strong, and the feet short and broad, resembling externally those of an elephant or tortoise. This family is mainly characteristic of the southern half of the American continent, but some species of the type genus ranged into Texas and Mexico. Many species of the family have been described and figured, especially by Burmeister (in the _Annales del Museo publico de Buenos Aires_), among which the following may be noticed. _Hoplophorus_ is characterised by the sculptured and frequently thin scutes of the carapace, those of the periphery being flat, and not raised into prominences. The caudal sheath has several overlapping movable rings at the base, and ends in a long subcylindrical terminal tube similar to the one represented with the carapace of _Glyptodon_ in Fig. 69, which in all probability really belongs to the genus under consideration. Each foot has four complete digits, and the humerus has an entepicondylar foramen. Most of the species are of medium size. Part of a caudal tube from Uruguay described as _Eleutherocercus_ indicates, however, a much larger allied form, in which the tail appears to have had a number of stout bristles protruding from the joints between the scutes. _Panochthus_ comprises very large Glyptodonts, distinguished by the great thickness of the scutes of the carapace, which are ornamented with tubercles. The termination of the caudal sheath forms a tube bearing large radiated tubercles. _Euryurus_ is distinguished by the radiate sculpture of the scutes of the carapace. _Dœdicurus_, of which one species was about twelve feet in length, also has a rugose sculpture on the carapace; but the termination of the caudal tube is expanded into a club-like shape, flattened from above downwards, and covered with tubercles mingled with a few large radiate discs, which, as in _Panochthus_, probably carried horny spines in the living condition. The typical genus _Glyptodon_ has each scute of the carapace ornamented with a rosette-like sculpture, the peripheral scutes being raised into conical prominences (Fig. 69). The caudal sheath, instead of being like the one represented in the figure, was entirely composed of a series of movable rings, ornamented with large tubercles. The manus had five digits, and the pes four; and there was an entepicondylar foramen to the humerus. A species of this genus, which attained very large dimensions, was made the type of _Schistopleurum_, on the supposition that the tail of _Glyptodon_ was of the type represented in Fig. 69. The genus _Thoracophorus_, of the Pleistocene of South America, as well as _Carioderma_, of the Pliocene of Texas, differ from all the preceding in having the scutes of the carapace in the form of disconnected nodules. Glyptodonts also occur in South American beds of earlier age than the Pleistocene, some of these forms having enamel bands on the teeth. “Why such a form as the Glyptodon should have failed to keep his ground is,” as the late Professor W. K. Parker remarks, “a great mystery; nature seems to have built him, as Rome was built, for eternity.”

[Illustration: FIG. 69.—_Glyptodon clavipes_ (Pleistocene, South America). From Owen. The tail is incorrectly restored, and it is probable that the figured portion belongs to _Hoplophorus_. The left lower corner shows an upper and a lower view of the skull, and the right a section of the caudal sheath.]

_Family_ MANIDÆ.

Covered externally (except the under surface of the body and inside of the limbs) with large imbricated horny scales, and scattered hairs growing in the intervals. No teeth. Tongue long, vermiform, and protractile. No accessory articular processes to the lumbar vertebræ, but the anterior zygapophyses largely developed and deeply concave, completely embracing the semicylindrical surfaces of the posterior zygapophyses. Limbs short, with five complete digits on each foot. Scaphoid and lunar bones of carpus united. Uterus bicornuate. Placenta diffused and non-deciduate. All the existing forms belong to the Ethiopian and Oriental regions of the Old World. The absence of additional articular processes to the lumbar vertebræ is a character in which this and the following family differ from all the preceding forms.

_Manis._[110]—Skull somewhat of the form of an elongated cone, with the small end turned forwards; very smooth and free from crests and ridges. No distinction between the orbits and temporal fossæ. The zygomatic arch usually incomplete, owing to the absence of the jugal bone. No distinct lachrymal bone. Palate long and narrow. The pterygoids extend backwards as far as the tympanics, but do not meet in the middle line below. Tympanic ankylosed to the surrounding bones, and more or less bullate, but not produced into a tubular auditory meatus. Rami of mandible very slender and straight, without any angle or coronoid process. From near the anterior extremity of the upper edge a sharp, conical, tooth-like process projects upwards and outwards. No clavicles. No third trochanter to the femur. Ungual phalanges bifid at their terminations. Caudal vertebræ with very long, strong transverse processes and numerous chevron bones. Tongue long, vermiform, flattened towards the tip; its retractor or sterno-glossal muscles arising from the hinder extremity of the immensely prolonged ensiform cartilage of the sternum. Stomach with thick lining membrane and muscular walls, and a special gland near the middle of the great curvature, consisting of a mass of complex secreting follicles, the ducts of which terminate in a common orifice. No cæcum. A gall-bladder. Head small, depressed, narrow, pointed in front, with a very small mouth-opening. Eyes and pinna of ear very small. Body elongated, narrow. Tail more or less elongated, convex above, flat underneath. The whole of the upper surface of the head, the upper surface and sides of the body, the whole of the tail, and the outer sides of the extremities covered with large, overlapping, horny scales, but usually with a few stiff hairs growing between and projecting beyond them. The sides and under surface of the head, the under surface of the body, and the inner sides of the limbs without scales, but with a rather scanty covering of hair. Limbs short. In walking the dorsal surface and outer sides of the phalanges of the two outer digits of the front feet alone rest on the ground, the points of the nails turning upwards and inwards. The third toe the longest, with a powerful compressed curved claw; the second and fourth with similar but smaller claws, that of the pollex often almost rudimentary. Hind feet plantigrade, with the hallux very short, and the four other toes subequal, with moderate, curved, subcompressed nails.

The reproductive organs of _Manis_ are of a totally different type from those of the families already noticed. The testes lie in the inguinal canal; and the penis is external and well developed. The uterus is truly bicornuate, the vagina not divided, and the placenta diffused and non-deciduate. All the organs and fœtal membranes are, indeed, formed very much on the plan of those of the Ungulates, without any trace of the special peculiarities obtaining in the typical American Edentates.

The animals of this genus, which includes all the existing forms, are called Pangolins or Scaly Anteaters, and are all of small or moderate size, terrestrial and burrowing, and feed mainly on termites. Several of them can climb trees. Their length varies from 1 to 5 feet. They can roll themselves up in a ball when in danger. Their peculiar elongated form, short limbs, long, gradually-tapering tail, and scaly covering give them on a superficial inspection more the appearance of reptiles than of mammals. The species are not numerous, and may be divided into two groups distinguished by a few not very important external characters; these groups also coinciding with the present geographical distribution of the genus. These two groups, according to Mr. O. Thomas, may be distinguished as follows.

The Asiatic pangolins are characterised by having the central series of body-scales continued quite to the extreme end of the tail, by having many isolated hairs growing up between the scales of the back, and by their small external ears. They all have a small naked spot beneath the tip of the tail, which is said to be of service as an organ of touch. There are three species, viz. _Manis javanica_, ranging from Burma, through Malacca and Java, to Borneo; _M. aurita_, found in China, Formosa, and Nipal; and the common Indian Pangolin, _M. pentadactyla_, distributed over the whole of India and Ceylon. The African species have the central series of scales suddenly interrupted and breaking into two at a point about 2 or 3 inches from the tip of the tail; they have no hair between the scales, and no external ear-conch. The following are the four species belonging to this group:—the Long-tailed Pangolin (_M. macrura_), which has a tail nearly twice as long as its body, and containing as many as forty-nine caudal vertebræ, being the largest number known among mammals; the White-bellied Pangolin (_M. tricuspis_), Fig. 70, closely allied to the last, but with longer and tricuspid scales, and white belly hairs. These two, like the Indian species, have a naked spot beneath the tail tip, a character probably correlated with the power of climbing, and they are, moreover, peculiar in having the outer sides of their fore legs clothed with hair, all the other species being scaly there as elsewhere. Lastly, the Short-tailed and the Giant Pangolins (_M. temmincki_ and _gigantea_), both of which have their tails covered entirely with scales, and evidently never take to arboreal habits. All the four species of the second group are found in the West African region, one only, _M. temmincki_, extending also into south and eastern equatorial Africa.

[Illustration: FIG. 70.—The White-bellied Pangolin (_Manis tricuspis_).]

According to Professor W. K. Parker,[111] who remarks upon the peculiarly aberrant nature of the group, the horny scales of the Pangolins really consist of cemented hairs. This writer states that “in the early embryo lozenge-shaped tracts of skin are seen all over its body, with lines of thinner cuticle between. Under the microscope, sections of these thicker tracts show that they are composed of fine hairs, cemented together by a copious growth of epidermic cells; here and there larger hairs are seen, but these fail to reach the surface, turning again towards the inside, like nails driven into wood that is too hard for their points.”

The same author also observes[112] that there are occasional instances of the presence of eight cervical vertebræ in the Pangolins—a feature which has been considered to indicate some former genetic connection between this family and the Sloths.

The following account of the habits of _Manis tricuspis_ is given by Mr. L. Fraser in his _Zoologia Typica_:—

“During my short residence at Fernando Po I succeeded in procuring two living specimens of this animal. The individuals, judging from the bones, were evidently not adult; the largest measured 30 inches in length, of which the head and body were 12 inches and the tail 18 inches. I kept them alive for about a week at Fernando Po, and allowed them the range of a room, where they fed upon a small black ant, which is very abundant and troublesome in the houses and elsewhere. Even when first procured they displayed little or no fear, but continued to climb about the room without noticing my occasional entrance. They would climb up the somewhat roughly hewn square posts which supported the building with great facility, and upon reaching the ceiling would return head foremost; sometimes they would roll themselves up into a ball and throw themselves down, and apparently without experiencing any inconvenience from the fall, which was in a measure broken upon reaching the ground by the semi-yielding scales, which were thrown into an erect position by the curve of the body of the animal. In climbing, the tail, with its strongly pointed scales beneath, was used to assist the feet; and the grasp of the hind feet, assisted by the tail, was so powerful that the animal would throw the body back (when on the post) into a horizontal position, and sway itself to and fro, apparently taking pleasure in this kind of exercise. It always slept with the body rolled up; and when in this position in a corner of the building, owing to the position and strength of the scales, and the power of the limbs combined, I found it impossible to remove the animal against its will, the points of the scales being inserted into every little notch and hollow of the surrounding objects. The eyes are very dark hazel, and very prominent. The colonial name for this species of _Manis_ is ‘Attadillo,’ and it is called by the Boobies, the natives of the island, ‘Gahlah.’ The flesh is said to be exceedingly good eating, and is in great request among the natives.”

The Indian species is said to live in pairs, and to give birth to one or two young at a time in the spring. Their burrow reaches a depth of some twelve feet, and terminates in a large chamber, which may be as much as six feet in diameter. A faint hiss appears to be the only sound emitted by these animals.

Remains of a large species of _Manis_, which are indistinguishable from the corresponding bones of the existing West African _M. gigantea_, are found fossil in cave-deposits in the Karnul district of Madras. This is one among several instances of the close connection between the Pleistocene and Pliocene mammalian fauna of India with the existing African fauna.

_Palæomanis._[113]—The lower Pliocene deposits of the Isle of Samos, in the Turkish Archipelago, have yielded remains of a Pangolin fully three times the dimensions of _M. gigantea_, upon the evidence of which the genus _Palæomanis_ has been established.

_Family_ ORYCTEROPODIDÆ

External surface scantily covered with bristle-like hairs. Teeth numerous, apparently heterodont, diphyodont, and of peculiar and complex structure, being traversed by a number of parallel vertical pulp-canals. Lumbar vertebræ with no accessory zygapophyses. Femur with a third trochanter. Fore feet without pollex, but all the other digits well developed, with strong moderate-sized nails, suited to digging, the plantar surfaces of which rest on the ground in walking. Hind feet with five subequal toes. Mouth elongated and tubular. Tongue subvermiform. Uterus bicornuate. Placenta broadly zonular. Feeding on animal substances. Terrestrial and fossorial in habits. Now mainly limited to the Ethiopian region.

_Orycteropus._[114]—The total number of permanent teeth appears to be from eight to ten in each side of the upper, and eight in the lower jaw; but they are never all in place at one time, as the small interior teeth are shed before the series is completed behind. In the adult they number usually five on each side above and below, of which the first two are simple and compressed, the next two larger and longitudinally grooved at the sides, the most posterior simple and cylindrical. The last three in either jaw having no milk-predecessors, may be regarded as true molars. The structure of all these teeth is quite peculiar among mammals, though resembling that of some fishes. Their summits are rounded before they are worn; their bases do not taper to a root, but are evenly truncated and continually growing. Each tooth is made up of an aggregation of parallel dental systems, having a slender pulp-cavity in the centre, from which the dentinal tubes radiate outwards, and being closely packed together each system assumes a polygonal outline as seen in transverse section. The small anterior teeth have milk-predecessors which are fully noticed below. Skull moderately elongated. The facial portion subcylindrical and slightly tapering. The zygoma complete and slender. The palate ends posteriorly in the thickened transverse border of the palatines, and is not continued back by the pterygoids. The tympanic is annular, and not ankylosed to the surrounding bones. The mandible is slender anteriorly, but rises high posteriorly, with a slender recurved coronoid, and an ascending pointed process on the hinder edge below the condyle, which is small, oval, and looks as much forwards as upwards. Vertebræ: C 7, D 13, L 8, S 6, C 27. The large number of lumbar vertebræ is peculiar among Edentates. Tongue less vermiform than in _Myrmecophaga_, being thick and fleshy at the base, and gradually tapering to the apex. The salivary apparatus is developed much in the same manner as in that genus, but the duct of the submaxillary gland has no reservoir. The stomach consists of a large subglobular cardiac portion, with a very thick, soft, and corrugated lining membrane, and a smaller muscular, pyloric part, with a comparatively thin and smooth lining. There is a very distinct ileo-cæcal valve, and a considerable-sized cæcum; also a gall-bladder. Head elongated, with a tubular snout, terminal nostrils, and small mouth-opening. Ears large, pointed, erect. Tail nearly as long as the body, cylindrical, very thick at the base, tapering to the extremity.

The reproductive organs and placentation of _Orycteropus_ are formed upon a principle unknown in the more typical Edentates, or, in combination, in any other mammals. Thus the testes, in the one described example, were inguinal, but appeared to descend, at all events temporarily, into a scrotum; but the penis is scarcely larger than that of the Great Anteater. The uterus is still more fully bicornuate than in _Manis_, with its two lateral chambers opening separately into the vagina, as in certain Rodents. The placenta is broadly zonary, but it is not known whether it is deciduate or not. It might readily be derived from the diffused placenta of _Manis_ by the abortion of the fœtal villi at the two poles of the ovum.

The _Orycteropodidæ_ have long been regarded as widely different from other Edentates, their presumed affinity with the _Manidæ_ being more or less problematical; but the discovery recently made by Mr. O. Thomas[115] that they have a milk-dentition still further emphasises their aberrant nature. According to this observer, it appears that there are normally no less than seven milk-teeth in the upper jaw, the hindmost of which is far larger than the others, having a rudimentary crown, and a distinct anterior and posterior root. The other milk-teeth are styliform, the four anterior ones being very minute, and separated from one another by equal intervals; the foremost of all is situated immediately behind the premaxillo-maxillary suture. In the mandible only four milk-teeth have hitherto been detected, of which the hindmost has the comparatively complex form found in the corresponding upper tooth. None of these milk-teeth appear, however, to cut the gum, so that the whole set is entirely functionless. Under the microscope these milk-teeth show signs of possessing a commencement of the remarkable histological structure found in the permanent teeth.

Mr. Thomas remarks that since “the three large posterior teeth of _Orycteropus_, already distinguished by their more molariform shape, do not have milk-predecessors, while all the small teeth anterior to them do, and in addition the last milk-tooth is markedly different from those in front of it, we ought apparently no longer to look upon this animal as an homodont, but instead to consider it as an originally heterodont form in which the incisors and canines have been suppressed to allow free play to the mobile vermiform tongue.

“But important as a knowledge of the presence of a milk-dentition in _Orycteropus_ is, it does not at present render any easier the difficult questions as to the phylogeny and systematic position of that animal. Although called an Edentate, it has always been recognised as possessing many characters exceedingly different from those of the typical American members of the order. It has in fact been placed with them rather on account of the inconvenience of forming a special order for its reception than because of its real relationship to them. Now, as they are either altogether toothless, or else homodont and monophyodont (apart from the remarkable exception of _Tatusia_), it seems more than ever incorrect to unite with them the solitary member of the Tubulidentata, toothed, heterodont, and diphyodont, and differing from them in addition by its placentation, the anatomy of its reproductive organs, the minute structure of its teeth, and the general characters of its skeleton.

“But if _Orycteropus_ is not genetically a near relation of the Edentates, we are wholly in the dark as to what other mammals it is allied to, and I think it would be premature to hazard a guess on the subject. Whether even it has any special connection with _Manis_ is a point about which there is the greatest doubt, and unfortunately we are as yet absolutely without any palæontological knowledge of the extinct allies of either. _Macrotherium_ even, usually supposed from the structure of its phalangeal bones, to be related to _Manis_, has lately proved to have the teeth and vertebræ of a perissodactyle Ungulate, and one could not dare to suggest that ancestors of _Manis_, or _Orycteropus_ were to be sought in that direction. Lastly, as the numerous fossil American Edentates do not show the slightest tendency to an approximation towards the Old World forms, we are furnished with an additional reason for insisting on the radical distinctness of the latter, whose phylogeny must therefore for the present remain one of the many unsolved zoological problems.”

The Aard-Varks (Earth-Pigs) as these creatures are commonly termed, from the name bestowed on them by the Dutch Boers of the Cape, are of nocturnal habits, sleeping during the day in their burrows, which are usually found in the neighbourhood of the tall hills or mounds made by termites. Indeed, wherever these hills are abundant it is stated there is a good chance of finding an Aard-Vark, the food of these animals consisting almost exclusively of termites and ants.

Two existing species are recognised, namely the Cape Aard-Vark (_O. afra_) from South Africa, and another (_O. æthiopicus_) from the north-eastern parts of Africa, ranging into Egypt. An extinct species has been described from the Lower Pliocene of the Isle of Samos, in the Turkish Archipelago, differing from the existing forms by the larger proportionate size of the lateral metatarsals.

_Bibliography of Edentata._—No general work on the order has been published since that of Rapp (_Anat. Untersuchungen über die Edentaten_, 2d ed. 1852). Among numerous memoirs on special groups the following may be cited:—_Myrmecophagidæ_:—R. Owen, “Anatomy of Great Anteater,” _Trans. Zool. Soc._ vol. iv.; G. Pouchet, _Mém. sur le Grand Fourmilier_, 1874; W. A. Forbes, “Anat. of Great Anteater,” _Proc. Zool. Soc._ 1882, p. 287. _Megatheriidæ_:—R. Owen, _Extinct Gigantic Sloth (Mylodon Robustus)_, 1842; Id., “On the Megatherium,” _Phil. Trans._ 1851-56; J. Leidy, “Extinct Sloth-tribe of North America,” _Smithsonian Contrib. to Knowledge_, vii. 1855; H. Burmeister, _Description de la République Argentine_, t. iii. Mammifères, 1879,—which contains full references to various memoirs by Owen, Gervais, Reinhardt, and others. _Glyptodontidæ_:—Owen, _Catalogue of Fossil Mammals, Mus. Roy. Coll. Surgeons_, 1845; T. H. Huxley, “Osteol. of Glyptodon,” _Phil. Trans._ 1865; H. Burmeister, _Annales del Museo Publico de Buenos Aires_, and _Descript. de la République Argentine_, 1879; H. Gervais and F. Ameghino, _Les Mammifères Fossiles de l’Amérique Méridionale_, Paris, 1880,—which also contains a list of all the S. American Edentates described at that date. _Dasypodidæ_:—J. Murie, “Anatomy of _Tolypeutes_,” _Trans. Linn. Soc._ vol. xxx. 1874; A. H. Garrod, _Proc. Zool. Soc._ 1878. For Placentation of Edentates see W. Turner, _Trans. Roy. Soc. Edin._ xxvii. (1873) p. 72, and _Journ. Anat. and Physiol._ vols. viii. and x.; A. Milne-Edwards, _Ann. Sciences Nat._ [6] viii. p. 1; and for brain, P. Gervais, “Formes cérébrales des Edentés,” _Nouv. Arch. du Muséum_, tom. v.; W. Turner, _Jour. Anatomy_, i. 313 (1867). For the dentition of _Orycteropus_ see O. Thomas, “A Milk Dentition in _Orycteropus_,” _Proc. Roy. Soc._ vol. xlvii. p. 246 (1890). Fuller observations on the mutual relations of the various families are given by W. H. Flower, “On the Mutual Affinities of the Animals composing the Order Edentata,” _Proc. Zool. Soc._ 1882, p. 358.