430 MAMMALIA [UKGULATA. a brachyodont to a hypsodont type. Loss of upper incisors. Development of canines into projecting tusks. Loss of anterior premolars. 2. As regards the limbs. Reduction of the ulna from a complete and distinct bone to a comparatively rudimentary state in which it coalesces more or less firmly with the radius. Keduction of the fibula till nothing but its lower extremity remains. Reduction and final loss of outer pair of digits (second and fifth), with coalescence of the metapodial bones of the two middle digits. Union of the navi- cularand cuboid, and sometimes theectocuueiform bone, of the tarsus. 3. Change of form of the odontoid process of the axis from a cone to a hollow half-cylinder. 4. Development of horns or antlers on the frontal bones, and gradual complication of form of antlers. 5. By inference only, increasing complication of stomach with ruminating function superadded. Modification of placenta from simple diffused to cotyledonary form. The primitive Artiodactyles, with the typical number (44) of incisor, canine, and molar teeth, brachyodont molars, conical odon toid process, four distinct toes on each foot, with metapodium and all carpal bones discrete, no frontal appendages, and (in all proba bility) simple stomach and diffused placenta, were separated even in the earliest known forms into Bunodonta and Selcnodonta. A. Bunodonta. This, the most primitive group, with various offsets which became partially specialized and then extinct, unable apparently to adapt themselves to new conditions, has been continued to the present day with comparatively little change in the section of the suborder called Suina, containing the families Hippopotamidee, and Suldaz. See HIPPOPOTAMUS, PECCARY, and SWINE. B. Selenodonta. Members of this group having the complete, typical dentition as regauls number, but with various modifications in the details of the form of the teeth, and also in the structure of the feet, abounded in the Middle and Upper Eocene and Lower Miocene of Europe and America. One of the earliest known, Anoplotherium, was fully described by Cuvier from remains found in the Paris gyp sum beds (Upper Eocene). Its teeth formed a series unbroken by a gap or diastema, and were of uniform height (as in Man alone of existing mammals). Its tail was long, with large chevron bones FIG. 110. Restoration of Anoplotherium commune (Upper Eocene). Cuvier. underneath, not usually found in Ungulates, and there were but two toes on each foot. It was in many respects a much specialized form, apparently not on the line of descent of any of the existing groups. Choeropotamus, Anthracotherium, Hyopotamus, Xiphodon, Dichodon, Dichobune, Cainotherium, the American Oreodon, and numerous others were forms more or less intermediate in character between the three distinct sections into which, by their extinction, the Selenodont Artiodactyles can now be divided, the Tylopoda, also called Phalangigrada, the Tragulina, and the Pecora or Cotylophora. I. TYLOPODA. Represented at the present time by the tVo species of Camels of the Old World and the Llamas of America. For their special dis tinguishing characters see articles LLAMA and CAMEL. II, TRAGULINA. No teeth in premaxillse. Upper canines well-developed, especi ally in the males ; narrow and pointed. Lower canines incisiform. No canmiform premolars in either jaw. Molariform teeth in a continuous series consisting of p f , m f . Odontoid process of axis conical. Fibula complete. Four complete toes on each foot. The middle metapodials generally confluent, the outer ones (second and fifth) very slender but complete, i.e., extending from the carpus or tarsus to the digit* Navicular, cuboid, and ectocuneiform bones of tarsus united. Tympanic bullae of skull filled with cancellar tissue. No frontal appendages. Ruminating, but the stomach with only three distinct compartments, the maniplies or third cavity of the stomach of the Pvcora being rudimentary. Placenta diffused. This section contains the single family Tragulidee, containing a few animals of small size, commonly known as C hevrotains, inter mediate in their structure between the Deer and the Pigs. The large size of the canines of the male and the absence of horns caused them to be associated formerly with Moschus, one of the true Deer ; hence they are often spoken of as "Pigmy Musk-Deer," although they have no musk-secreting gland, or, except in the above-named trivial external characters, no special affinities with the true Musk. There has scarcely been a more troublesome and ob durate error in zoology than in this association of animals so really distinct. It has been troublesome, not only as preventing a just conception of the relations of existing Artiodactyles, but also in causing great confusion and hindrance in palaeontological researches among allied forms ; and most obdurate, inasmuch as all that has been recently done in advancing our knowledge of both groups has not succeeded in eradicating it, not only from nearly every one of our zoological text-books, whether British or Continental, but even from works of the highest scientific pretensions. The family is now generally divided into two genera. Tragulus, containing the smallest of the existing Ungulates, animals having more of the general aspects and habits f some Rodents, as the Agoutis, than of the rest of their own order. The best-known species are T. javanicus, T. napu, T. kanchil, T. stanleyanus, and T. mcmmina. The first four are from the Malay Peninsula, or the islands of the Indo-Malayan Archipelago, the last from Ceylon and Hindustan, Hyomosclms is distinguished chiefly by the feet being stouter and shorter, the outer toes better developed, and the two middle meta- carpals not ankylosed together. Its dental formula (as that of Tragulus) is i ,- c{,p%, mf = 34. Vertebrse : C7, D 13, L6, S5, C 12-13. The only existing species, H. aquaticus (fig. Ill), from the west coast of Africa, is rather larger than any of the FIG. 111. African Water Chevrotain (Hyomoschus aquaticus). Asiatic Chevrotains, which it otherwise much resembles, but it is said to frequent the banks of streams, and have much the habits of Pigs. It is of a rich brown colour, with back and sides spotted and striped with white. It is evidently the survivor of a very ancient form, as remains of a species only differing in size (H. cra-ssus) have been found in Miocene deposits at Sansan, depart ment of Gers, France. III. PECORA or COTYLOPHORA. No premaxillary teeth or caniniform premolars. Upper canines generally absent, though sometimes largely developed. Inferior incisors, three on each side with an incisiform canine in contact with them, Molariform teeth consisting of p f, m f, in con tinuous series. Auditory bullae simple and hollow within. Odon toid process in the form of a crescent, hollow above. Distal extremity of the fibula represented by a distinct malleolar bone of peculiar shape, articulating with the outer surface of the lower end of the tibia. Third and fourth metacarpals and metatarsals con fluent. Outer toes small and rudimentaiy, or in some cases entirely suppressed; their metapodial bones never complete. Navicular and cuboid bones of tarsus united. Horns or antlers usually present, at least in the male sex. Left brachial artery arising from a common innominate trunk, instead of coming off separately from the aortic arch as in the preceding sections. Stomach with four complete
cavities. Placenta cotyledonous.