while there may be traces of an anterior ridge. The premolars are simpler. Lambdotheriida.-This family is confined to the Upper Eocene and Miocene of North America, where it is represented by Lambdotherium, Palæosyops, and Limnosyops; it presents the normal type of foot structure, and all the genera except the first have the full complement of teeth. There were four digits in the manus. The last lower molar has a third lobe. Limnosyops differs from Palæosyops in having two inner columns to the last upper molar. Chalicotheriida.-The genus Chalicotherium, which is found in the Tertiaries of Europe, Asia, and North America, differs so remarkably in the structure of the feet from all other Ungulates that it has been proposed to regard it as the representative of a distinct order, Ancylopoda. The molars are, however, almost indistinguishable from those of the preceding and following families; while the cervical vertebræ and portions of the limbs are of a Perissodactyle type. On the other hand, the femur has lost its third trochanter; while the phalanges are strangely modified, the terminal ones forming long curved claws, while the others (Fig. 175) have strong ginglymoid distal articulations. These phalanges were, indeed, species of Chalicotherium is dis FIG. 175.-Anterior and distal aspects of a phalangeal bone of Chalicotherium sivalense. (From the Paleontologia Indica.) tinguished by the loss of the incisors and the upper canine; while all the species want the first premolar. Titanotheriida.-This exclusively North American family includes gigantic forms closely allied to the Lambdotheriida, but with the last upper premolar as complex as the molars, and frequently with large bony protuberances in the nasal region. The best known genus, Titanotherium (Menodus, Brontotherium, Symborodon, Allops, etc.), may either have the full complement of teeth, or the incisors may be reduced to. The canines and incisors are small, and there is no diastema when the full dental series is developed. The skull is very like that of the Rhinoceroses; but has a transverse pair of large bony prominences on the nasal region, varying considerably in shape and size in the different species, which in the living animal were probably covered with horny sheaths. The third 1 This name is the earliest, but is preoccupied. trochanter of the femur was aborted. These huge animalsinferior in size only to the Elephant-appear to have been abundant in the United States during the Miocene period. Family MACRAUCHENIIDÆ. This extinct South American family is best known by the genus Macrauchenia, as represented by M. patachonica and M. boliviensis, which are apparently from Pleistocene formations. They are very singular and specialised forms, quite out of the line of descent of any of the existing Perissodactyles, and the steps by which they are connected with the rest of the group have not yet been discovered. Of the larger species, M. patachonica, the skeleton is completely known. It had the full number of forty-four teeth, forming an almost uninterrupted series. The cervical vertebræ resemble those of the Camels in the position of the vertebrarterial canal, but the ends of the centra are flat, and not opisthocœlous as in the allied forms. In some of the limb characters it resembles the Equide, but in the articulation of the fibula with the calcaneum it agrees with the Artiodactyles. The structure of the feet is, however, distinctly Perissodactylate, there being three toes on each. The teeth approximate to a Rhinocerotine structure; and the incisors have an infolding of the enamel of their crowns, as in those of the Horses. The nares open on the top of the skull, and it is probable that the muzzle was produced into a short proboscis. Several other South American forms have been referred to this family, some of which have received distinct generic names, but further evidence is required before many of them can be accepted. Possibly Homalodontotherium should be placed here. Family PROTEROTHERIIDE. Proterotherium.-Here may be noticed certain very remarkable Perissodactyles from the South American Tertiaries, for which the name Proterotherium has been proposed. The cheek-teeth are so like those of Anchitherium that they have been described under that name. The upper jaw has one pair of canine-like incisors and no canines, while the lower jaw carries two pairs of incisors. In the skull the orbits were completely closed, as in the Horses. The feet were tridactyle, like those of Hipparion, but the tarsus was constructed on an Artiodactyle type. SUBUNGULATA. By far the greater number of the Subungulata are extinct, and of many of those whose former existence has been revealed, chiefly by the labours of the American palæontologists, our knowledge is at present necessarily imperfect, though daily extending. It will only be possible here to give details of some of the more interesting or best-known forms. The characters by which the skeleton of the feet of the Subungulata are distinguished from those of the Ungulata Vera have been already mentioned on p. 275. In addition to these it may be observed that the feet frequently have five functional digits, and may be plantigrade; while the upper surface of the astragalus is generally flattened, instead of presenting the strongly-marked pulley-like ridges and groove so characteristic of the Ungulata Vera. Suborder HYRACOIDEA. Family HYRACIDE. This division is constituted to receive a single family of mammals, the affinities of which have long constituted a puzzle to zoologists. They were first placed among the Rodents, to which animals their small size and general appearance and habits give them much superficial resemblance. Cuvier's investigations into their anatomical structure, and especially their dental characters, led him to place them among the Ungulates, near the genus Rhinoceros, a position long accepted by many zoologists. Further knowledge of their organisation and mode of development caused Milne-Edwards, Huxley, and others to disassociate them from this connection, and, failing to find any agreement with any other known forms, to place them in an order entirely apart. Palæontology has thrown no light upon the affinities of this anomalous and isolated group, as no extinct animals possessing their distinctive characters have as yet been discovered. The dentition, according to the usual interpretation, consists only of incisors and molars, the formula in all known species being i 1, c 8, p 4, m . The upper incisors have persistent pulps, and are curved longitudinally, forming a semicircle as in Rodents. They are, however, not flattened from before backwards as in that order, but prismatic, with an antero-external, an antero-internal, and a posterior surface, the first two only being covered with enamel; their apices are consequently not chisel-shaped, but sharp pointed. They are preceded by functional, rooted milk-teeth. The outer lower incisors, which should perhaps be regarded rather as canines, have long tapering roots, but not of persistent growth. They are straight, procumbent, with awl-shaped, trilobed crowns. Behind the incisors is a considerable diastema. The molars and premolars are all contiguous, and formed almost exactly FIG. 177.-Skull and dentition of Dendrohyrax dorsalis. x 3. on the pattern of some of the Perissodactyle Ungulates. The hyoid arch is unlike that of any known mammal. The dorsal and lumbar vertebræ are very numerous, 28 to 30, of which 21 or 22 bear ribs. The tail is extremely short. There are no clavicles. In the fore foot the three middle toes are subequally developed, the fifth is present, but smaller, and the hallux is rudimentary, although, in one species at least, all its normal bones are present. The ungual phalanges of the four outer digits are small, somewhat conical, and flattened in form. The carpus has a distinct os centrale. There is a slight ridge on the femur in the place of a third trochanter. The fibula is complete, thickest at its upper end, where it generally ankyloses with the tibia. The articulation between the tibia and astragalus is more complex than in other mammals, the end of the malleolus entering into it. The hind foot is very like that of Rhinoceros, having three well-developed There is no trace of a hallux, and the fifth metatarsal is represented only by a small nodule. The ungual phalanx of the toes. inner (or second) digit is deeply cleft, and has a peculiar long curved claw, the others have short broad nails. The stomach is formed upon much the same principle as that of the Horse or Rhinoceros, but is more elongated transversely and divided by a constriction into two cavities-a large left cul de sac, lined by a very dense white epithelium, and a right pyloric cavity, with a very thick, soft, vascular lining. The intestinal canal (Fig. 178) is long, and has an arrangement per- ст FIG. 178.-Diagrammatic view of the alimentary canal of Hyrax capensis, the intestines being somewhat abbreviated. d, Duodenum; i, ileum; cm, cæcum; c, supplemental colic cæca; r, rectum. Rodents. The female has six teats, of which four are inguinal and two axillary; and the placenta is zonary, as in the Elephant and Carnivora. There are two distinct forms of Hyrax, differing both in structure and habits, which may be accorded generic rank. Hyrax.-Molar teeth having the same pattern as those of 1 Hermann, Tab. Affinit. Anim. p. 115 (1783). It has recently been proposed to substitute the earlier name Procavia in lieu of Hyrax. The anatomy of Hyrax was first described by Pallas (Spicilegia Zoologica). Besides minor memoirs, two detailed accounts of its structure have appeared-one by Brandt, in Mém. Acad. Nat. Scien. St. Pétersbourg, 7ième sér. vol. xiv. No. 2, 1869; and |