Page:Encyclopædia Britannica, Ninth Edition, v. 15.djvu/402

Rh 380 MAMMALIA [MARSUPIALIA. B. All the teeth with persistent pulps. Incisors f, large, scalpri- form, with enamel on the outer surface only. No canines. Hind feet with four subequal outer toes ; partially syndactylous and with rudimentary hallux. 6. Phascolomyidse. Family DIDELPHID^E. Dentition : i%, c, p |, m f ; total 50. Incisors very small and pointed. Canines large. Premolars with compressed pointed crowns. Molars with numerous sharp cusps. The third premolar preceded by a deciduous multicuspidate molar, which remains in place until the animal is nearly adult. Limbs of moderate develop ment, each with five complete and distinct toes, all of which are provided with short, compressed, curved, sharp claws of nearly equal size, except the first toe of the hind foot or hallux, which is large, widely separable from the others, to which it is opposed in climbing, and terminates in a dilated rounded extremity, without a nail. Tail generally long, partially naked and prehensile. Stomach simple. Caecum of small or moderate size. Pouch in some complete, in others represented by two lateral folds of the abdominal integument, partially covering the teats, while in some all trace of it is absent. Vertebra : C 7, D 13, L 6, S 2, C 19-35. The Didclphidse, or true Opossums, differ from all other Marsu pials in their habitat, being peculiar to the American continent. They are mostly carnivorous or insectivorous in their diet, and arbo real in habits. One slightly aberrant form, with webbed hind feet, and aquatic mode of life, constitutes the genus Chironectcs. The other numerous species are commonly included in the genus Di- delphys. See OPOSSUM. Family Dentition : i -f, c |, p and m numerous, variable. Incisors small ; canines well developed ; molars with pointed cusps. Limbs equal. Fore feet with five subequal toes with claws. Hind feet with the four outer toes well-developed, and distinct from each other and bearing claws ; the first (or hallux) clawless, generally rudimentary, sometimes entirely wanting. Stomach simple. No caecum. Predatory, carnivorous or insectivorous animals, inhabitants of Australia, Tasmania, and the southern parts of New Guinea and some of the adjacent islands. The aberrant genus MyrmecoMus, though clearly a member of this family, is so sharply distinguished from all the others as to render a division into two subfamilies necessary. Subfamily Dasyurinse. This comprises the more typical Dasyuridee, in which the premolars and molars never exceed the normal number of seven on each side of each jaw, and in which the tongue is not specially extensile. Thylacinus. Dentition: i%, c, p f, in | = 46. Incisors small, vertical, the outer one in the upper jaw larger than the others. Summit of the lower incisors, before they are worn, with a deep transverse groove, dividing it into an anterior and a posterior cusp. Canines long, strong, and conical. Premolars with compressed crowns, increasing in size from before backwards. True molars in general characters resembling those of Dasyurus, but of more simple form, the cusps being not so distinct nor sharply pointed. Milk FIG. 26. Thylacine (Thylacinus cynocepkalus). molar very small, and shed before the animal leaves the mother s pouch. General form very Dog-like. Head elongated. Muzzle pointed. Ears moderate, erect, triangular. Fur short and closely applied to the skin. Tail of moderate length, thick at the base and tapering towards the apex, clothed with short hair. Hallux (including the metacarpal bone) wanting. Vertebra} : C 7, D 13, L 6, S 2, C 23. Marsupial bones represented only by small unossified fibro-cartilages. The only known species of this genus, T. cynweplialus, though smaller than a common Wolf, is the largest predaceous Marsupial at present existing. It is now entirely confined to the island of Tasmania, although fragments of bones and teeth found in caves afford evidence that a closely allied species once inhabited the Australian mainland. The general colour of the Thylacine is grey- brown, but it has a series of transverse black bands on the hinder part of the back and loins, whence the name of &quot;Tiger &quot; frequently applied to it by the colonists. It is also called &quot;Wolf,&quot; and some times, though less appropriately, &quot; Hyaena.&quot; Owing to the havoc it commits among the sheepfolds, it has been nearly exterminated in all the more settled parts of Tasmania, but still finds shelter in the almost impenetrable rocky glens of the more mountainous regions of the island. The female produces four young at a time. Dasyurus. Dentition : i f-, c j-, p f, m | ; total 42. Upper incisors nearly equal, and placed vertically. In the smaller species the first is slightly longer, narrower, and separated from the rest. Lower incisors nearly vertical in the larger, but sloping forwards and upwards in the smaller species. Canines large and sharply pointed. Premolars, in the typical forms, with compressed and sharp-pointed crowns, and slightly developed anterior and posterior accessory basal cusps. True molars with numerous sharp-pointed cusps. In the upper jaw the first three with crowns having a triangular free surface, the fourth small, simple, narrow, and placed transversely. In the lower jaw the molars more compressed, with longer cusps ; the fourth not notably smaller than the others. Ears of moderate size, prominent, and obtusely pointed. Hallux rudimentary, clawless, or absent ; its metatarsal bone always pre sent. Tail generally long and well clothed with hair. Vertebra: : C 7, D 13, L 6, S 2, C 18-20. The true Dasyures are mostly inhabitants of the Australian continent and Tasmania, where in the economy of nature they take the place of the smaller predaceous Carni- vora, the Cats, Civets, and Weasels of other parts of the world. They hide themselves in the daytime in holes among rocks or in hollow trees, but prowl about at night in search of the small living mammals and birds which constitute their prey. .The species are not numerous, and divide themselves into two sections. (1) Dasyurus proper includes D. maculatus, about the size of a com mon Cat, inhabiting Tasmania and the southern part of Australia ; D. viverrinus or maugei, Tasmania and Victoria ; D. gcoffroyi, South Australia ; D. hallucatus, North Australia ; D. allopunctatus, New Guinea. (2) Sarcophilus contains one species, D. ursinus, differ ing from the others in being a larger and heavier animal, with a disproportionally large and broad head. Its teeth are relatively larger and more massive, and hence more crowded in the jaws ; the premolars especially are scarcely compressed but rather conical ; the lower molars want a cusp placed near the middle of the inner border, found developed in different degrees in all the species of the first section. This animal is peculiar to Tasmania, where it is commonly known by the name of &quot;Devil.&quot; Its prevailing colour is black, its size about that of an English Badger, and its disposition remarkably savage and voracious. Phascogale. This genus (more properly Pliascologale) comprises a considerable number of small Marsupials, none of them exceeding a common Rat in size, differing from the true Dasyures in pos sessing an additional premolar, the dentition being i, cf, p, ?)i f; total 46, and having the teeth generally developed upon an insectivorous rather than a carnivorous pattern, the upper middle incisors being larger and inclined forwards, the canines relatively smaller, and the molars with broad crowns, armed with prickly tubercles. The muzzle is pointed. Ears moderately rounded anil nearly naked. Fore feet with five subequal toes, with compressed, slightly curved pointed claws. Hind feet with the four outer toes subequal, with claws similar to those in the fore feet ; the hallux almost always distinct and partially opposable, though small and nailless, sometimes absent. The food of these animals is almost entirely insects, which some pursue among the branches of trees, while others are purely terrestrial. They are found throughout Australia, and also in New Guinea and the Aru and some of the adjacent islands. Variations in the details of the dentition and of the structure of the hind limbs, and in the length and arrange ment of the hairy covering of the tail, have given rise to several subdivisions which will probably be accepted as generic by most zoologists, although further investigations are required before their limits can be very satisfactorily defined. P. cristieauda, a species with a thick compressed tail orna mented upon its apical half with a crest of black hair, differs from the others by the very reduced size of the third premolar in the upper and its complete absence in the lower jaw, thus forming an interesting transition in dentition towards Dasyurus. It consti tutes the genus Chxtoccrcus of Krefft. Another very aberrant form, P. lanigera, distinguished by the great elongation of the fore arm and hind foot, and the complete absence of hallux, is Antechinomys of thf same author. It is an elegant little terrestrial mouse-like animal, with large oval ears and long tail with the terminal part bushy. Antichinus and Podabrus are names proposed for other divisions of the group.