MARSUPIALIA, ( Marsupium, a pouch,) Eng. Marsupials; Fr. Marsupiaux; Ger. Bea. tel t h iere.
Essential external character.—Mammalian quadrupeds, distinguished by a peculiar pouch or duplicature of the abdominal integument, which, in the males, is everted and contains the testes ; in the females is inverted, covering the mammm, and generally sheltering the young for a certain period after their birth.
Essential internal character.—In both sexes two supplementary trochlear bones are articu lated to the anterior part of the brim of the pelvis, around which play the muscles em bracing and supporting the testes in the male, and the mammary glands in the female ; these bones, from their connexion with the pouch, are called " marsupial." The quadrupeds associated together by the common external and osteological characters above defined, are ovo-viviparous or impla cental,* the vascular layer of the allantois not being developed, so as to organize the villi of the chorion, or to form cotyledons or a pla centa. The marsupial also differ from the placental Mammalia in other important parts of internal organization, as in the structure of the brain and of the heart, and in the con dition of the sanguiferous and absorbent sys tems; and they present remarkable modifica tions of the genital apparatus in both sexes.
Classification.—The Marsupial animals are generally of small size; some, as the Pigmy Opossum (Petaurus pygnueus), and Dwarf Pbalanger ( Phalangista nana), are less than the common mouse : the largest known existing species is the common or Great Kangaroo ( Marropus major). With the exception of the Virginian Opossum, all the Marsupialia are confined to the southern hemisphere of the globe, and they are principally natives of Aus tralasia, to which part of the world several remarkable genera are peculiar, and where, with a few exceptions, as certain Cheiroptera and a few Rodent genera, as Hydromys, Hapalatis, and Pseudomys, all the known aboriginal mammals are Marsupial or Monotrematous.t It is in the Australian continent that we per ceive the Marsupial quadrupeds typifying, so to say, or playing corresponding parts with those allotted to the placental Mammalia in a larger theatre of the habitable surface of the earth. The carnivorous Thylacines* and Da syuresit for example, are the pignfidestruc tires of the country, committing occasional ravages among the sheep and poultry, but not disdaining dead animal matter or garbage.
The species of Phascogale, Myrmecobius, and Perameles represent the placental Insec tivora. Many Marsupials which live in trees have an omnivorous or vegetable diet ; these in their prehensile tail and hinder thumb typify the Quadrumana ; and one species, the tailless Koala, seems to represent the American sloths or the arboreal sun-bears of the Indian Archi pelago.
Another species of Marsupial, the Wom bat, presents the dentition which characterizes the placental Itodentia ; and the Petaurists, like the flying squirrels, have a parachute formed by broad duplications of the skin ex tending laterally between the fore and hind legs.
The Kangaroos are the true herbivorous Marsupialia, and many interesting physiolo gical conditions present themselves to the mind in contemplating the singular construction and proportions of these animals. It would ap pear that the peculiarities of their gestation rendered indispensably necessary the posses sion of a certain prehensile faculty of the anterior extremities, with a free movement of the digits and a rotatory power of the fore-arm, in relation to the manipulations of the pouch and of the embryo therein protected and ma tured. At the same time an herbivorous quad ruped must possess great powers of locomo tion in order to pass from pasture to pasture, and to avoid its enemies by flight. These powers, as is well known, are secured to the herbivorous species of the placental Mammalia by an ungulate structure of four pretty equally developed members. Such a structure, how ever, would have been incompatible with the procreative economy of the Kangaroo. It is, therefore, organized for a rapid course by an excessive development of the hinder extre mities, and these alone serve the animal in flight, which is performed by a succession of extensive bounds. The tail, also, is of great power and length, and, in the stationary po sition, the body is supported erect on the tripod formed by the tail and hind legs, while in easy progression the tail serves as a crutch, upon which and the fore feet the body is sustained while the hind legs are swung forwards.