Page:Encyclopædia Britannica, Ninth Edition, v. 15.djvu/411

Rh SIRENIA.] 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 anterior 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 structure of all these teeth is quite peculiar among mammals, though resembling that of some tishes. 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. No evidence of any vertical succession of teeth has been dis covered. Skull moderately elongated. The facial portion sub- cylindrical 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 forwards as much as upwards. Vertebra;: C7, D13, L8, S6, C25. The large number of lumbar vertebra; is peculiar among Edentates. Tongue less vermiform than in Mynnecophaga, being thick and fleshy at the base, and gradually tapering to the apex. The salivary apparatus is developed much in tlie same manner as in that genus, but the duct of the submax- illary gland has no reservoir. The stomach consists of a large sub- globular cardiac portion, with a very thick, soft, and corrugated lining membrane, and a smaller muscular, pyloric part, with a compara tively thin and smooth lining. There is a very distinct ileo-coecal valve, and a considerable-sized crecum ; also a gall-bladder. No pollex to the fore foot. All the other usual toes well developed, with strong, subcompressed nails, flatter on the hind foot. 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 best known species is the Cape Anteater (0. cajmisis), or &quot;Aard-Vark&quot; (Earth Pig) of the Dutch colonists, from Soutli Africa, an animal not altogether unlike a Pig in size and general appearance. It lives in burrows in the ground, and feeds chiefly on ants and other insects. A second species, or well-marked local variety, 0. sethiopicus, inhabits the north-eastern parts of Africa. EXTINCT EDENTATA OF THE OLD &quot;WORLD. Certain remains, chiefly of bones of the limbs, found in France and Greece, and assigned to genera called Macothcrium and Ancy- lotlbcrium, united provisionally in the family Macrot/iemulse, indi cate the existence of animals of large size inhabiting Europe during the Middle Tertiary epoch, the characters of which appear to in dicate a generalized Edentate form or something intermediate between the Edentata and Ungulata. In the structure of the phalanges they most resembled the Manvlse., but there is some evi dence that they possessed teeth. Some fragments from the Eocene of Paris are still more doubtfully assigned by Gervais to the order. Bibliograph y of Edenta a. No general work on the order has been published tout that of V.Ati {Anat. Untersuchungcn ilber die Edentaten, 2d ed., 1852), now nearly out of date. Among numerous memoirs on special groups the following may bo cited : Myrmecophagidx : R. Owen, &quot;Anatomy of Great Anteater,&quot; Trans. Zoo!. Soc., vol. iv. ; G. Pouchct, Mem. sitr le Grand Fovrmilier,1874; W. A. Forbes, &quot;Anat. of Great Anteater,&quot; Proc. Zool. S./c., 1882, p. 287. Mega- theriidx : R. Owen, Extinct Gigantic S oth (Mylodon Robustu s), 1842 ; Id., &quot;On the Megatherium,&quot; Philos. Trans., 1851-56 ; J. Leidy, &quot;Extinct Sloth-tribe of North America,&quot; Smithsonian Contrib. to Knowledge, vii., 185o ; II. Burmcister, Description de la Republique Argentine, t. iii. Mammiferes, 1879, which con tains full references to various mem. d is by Owen, Gervais, Reinhardt, and others. Glyptodontidx : Owen, Catalogue of Fossil Mammals, Mus. Roy. Coll. Surgeons, 1845; T. II. Huxley, &quot; Osteol. of Glyptodon,&quot; Phil. Trans., 1865 ; IT. Burmcistcr, Annales del Museo Publico de Buenos Ayres, and De&cript. (le la Re publique Argen tine, 1879. Dasypodidx : J. Muric, &quot; Anatomy of Tolypcutes.&quot; Trans. Linn. Soc., vol. xxx., 1874 ; A. II. Garrod, Proc. Zool. Soc., 1878. For placcntati nof Eden tates see W. Turner, Trans. Roy. S-.c. Edin., xxvii. (1873) p. 72, and Jour. Anat. and Physio!., vols. viii. and x. ; A. Milne-Edwards, Ann. Sciences Nat. [f&amp;gt;] viii. p. 1 ; and for brain, P. Gervais, &quot; Formes cerdliralcs des Edentds,&quot; Nouv, Arch, du Museum, torn. v. ; W. Turner, Jour. Anatomy, i. 313 (1867). ORDER SIRENIA. The purely aquatic habits and Fish-like form of the animals of this order caused them to be formerly con founded with the Cetacea, but a more intimate knowledge of their structure has shown that they really belong to a widely different type of the class. The head is rounded and not disproportionate in size as compared with the trunk, from which it is scarcely separated by any externally visible constriction or neck. ALIA 389 Nostrils valvular, separate, and placed above the fora part of the obtuse, truncated muzzle. Eyes very small, with imperfectly formed eyelids, capable, however, of contraction, and with a well-developed nictitating mem brane. Ear without any pinna. Mouth of small or moderate size, with tumid lips beset with stiff bristles. General form of the body depressed fusiform. No dorsal fin. Tail flattened and horizontally expanded. Fore limbs paddle-shaped, the digits being enveloped in a common cutaneous covering, though sometimes rudiments of nails are present. No trace of hind limbs. External surface covered with a tough, finely wrinkled, or very rugous skin, naked, or with fine hairs sparsely scattered over it. The skeleton is remarkable for the massiveness and density of most of the bones of which it is composed, especially the skull and ribs, which must add to the specific gravity of these slow-moving animals, and aid in keeping them to the bottom of the shallow waters in which they dwell, while feeding on aquatic vegetables. The skull presents many peculiarities, among which may be indicated the large size and backward position of the anterior narial aperture, a further modification of that met with in the Tapirs amo4ig Ungulates, and presenting some approach to that so characteristic of the Cetacea. The nasal bones are generally absent in the recent forms, or are only found in a most rudimentary condition, attached to the edge of the frontals, far away from the middle line ; but in some at least of the extinct species these bones, though small in size, are normal in situation and relations. In very few other respects does the skull present any resemblance to that of the Cetacea. In the spinal column none of the vertebra? are united together to form a sacrum, and the flat ends of the bodies do not ossify separately, so as to form disk-like epiphyses in the young state, as in nearly all other mammals. The anterior caudal vertebrae have well-developed chevron bones. In one genus (Manatus) there are only six cervical vertebrae. There are no clavicles. The humerus has a small but distinct trochlear articulation at the elbow-joint. The two bones of the forearm are about equally developed, and generally ankylosed together at both extremities. The carpus is short and broad, and the digits five in number, with moderately elongated and flattened phalanges, which are never increased in number beyond the limit usual in the Mammalia. The pelvis is extremely rudimentary, consist ing of a pair of bones suspended at some distance from the vertebral column. In no existing species is there any trace of a hind limb, but in the extinct Halitherium an acetabular depression and rudimentary femur have been discovered. ; Two kinds of teeth, incisors and molars, separated by a wide interval, are generally present. The former may be developed into tusks in the upper jaw, or may be quite rudimentary. The molars vary much in character. In one genus (Eytina) no teeth of any kind are present, at least in the adult. In all, the anterior part of the palate, and a corresponding surface on the prolonged symphysis of the lower jaw, are covered with rough horny plates of peculiar structure, which doubtless assist in mastication. The tongue is small and fixed in position, with a surface resembling that of the plates just spoken of. The salivary glands are largely developed. The stomach is compound, being divided by a valvular constriction into two principal cavities, the first of which is provided with a singular glandular pouch near the cardiac end, and the second usually with a pair of elongated, conical, coacal sacs or diverticula. The intestinal canal is long, and with very muscular walls. There is a caecum, either simple, conical, and with extremely thick walls, as in Halicore, or bifid, as