Marsipials, an order of implacental mammals, all, with the exception of the American opossums, now confined to Australia and its archipelago. The name is derived from the presence of a marsupium or abdominal pouch in the females for the protection of their immature young, supported by two supplementary bones attached to the anterior margin of the pelvis. The cerebral characters have been described under Mammalia, and the peculiarities of the marsupial lactation under Kangaroo. They have been divided into two sections, according to the character of their food, the phytophagous or plant-eating and the rapacious or carnivorous and insectivorous groups. The former are characterized by the small size or absence of canine teeth, the large incisors (never more than two in the lower jaw), and broad tubercular molars; they include the three families of phascolomyda or wombats, macropodidae or kangaroos, and pha-larigistidce or phalangers and koala. The sec-ond group have small and numerous incisors, eight to ten in the upper and six to eight in the lower jaw, canines large and in both jaws, and pointed molars; they include the four families of peramelida or bandicoots, didel-phidae or opossums, myrmecohiida or Australian ant-eaters, and dasyurida or dasvures, the last the most carnivorous of all in habits and form.
This order presents animals -howing types of many of the placental orders; for instance, the phalangers call to mind thequadru-mana, the dasvures the carnioora, the phasco-gales the imectirora, and the kangaroos the edentata. Though Australia is the great headquarters of the marsupials, they are found in America from the middle United States to Buenos Ayres, as well as on the W. coast of South America: those species in Australia nearlv allied and with similar habits do not appear to he associated in the same limited district. - The skull in marsupials presents the reptilian character of permanent separation of the hones, even in old animals; the palate is very imperfect, and the angle of the jaw bent inward; the number of teeth is greater than in placental mammals, and that of the incisors is never the same in each jaw; clavicles are present in must of the species; the marsupial bones, existing in both sexes, are considered by Owen as trochlear or sesamoid bones, developed in the tendon of the external oblique muscle of the abdomen as the knee-pan is in the tendon of the rectus of the thigh, the cremaster muscle winding around them in the male and the compressors of the mammary gland in the female; in many genera, like the opossums, the tibia and fibula are so loosely connected with each other and with the tarsus that the foot has a movement of rotation upon the leg, the inner toe acting as an opposable thumb.
The brain, relatively to the body, is smaller in marsupials than in any other mammal-, varying between 1 to 520 and 1 to 800; its structure is more simple, and its surface without convolutions or corpus callosum, and the intelligence corresponds to this inferiority of cerebral development. The organs of smell, hearing, and other senses are well developed; the eyes are generally large and prominent, as most of them are nocturnal in their habits. There are three modifications of the stomach, it being simple in the opossums and phalangers, with a glandular apparatus in the koala and wombat, or sacculated in the kangaroos (in the latter resembling in structure the human colon); these modifications do not appear to be related to the character of the food; in the genera with a simple stomach the caecum is much developed, being sometimes three or four times us long as the animal, while it is very small in those with sacculated complex stomachs, showing the vicarious functions of these two portions of the alimentary canal; in the flesh-eating marsupials the intestine is suspended on a simple and continuous mesentcrv, a- in carnivorous reptiles.
The liver is divided into many lobes, and is always provided with a gall bladder; the pancreas and spleen are triangular or T-shaped; in the heart there is not the usual trace of the fcetal communication between the auricles, on account of the earlv period at which the incompletely developed young begin to respire air. The lungs are constructed on the usual mammalian type, the only tendency to the oviparous structure being the entireness of the rings of the trachea in some of the phalangers; the kidneys present nothing unusual; the membranous portion of the urethra is longer and wider than in other mammals; the resicules seminalen are absent, and the glans sometimes double, with a corresponding duplication in the female organs-in these ovo-viviparons or implacental mammals the vascular layer of the allantois is not developed so as to organize the villi of the chorion or to form cotyledons or a placenta. For details on the anatomy, mode of development, and natural history of marsupials, the reader is referred to the article "Marsupialia," by Owen, in vol. iii. of the "Cyclopaedia of Anatomy and Physiology," and to vol. i. of the "Natural History of Mammalia," by G. R. Waterhouse (London, 1846). Prof. Owen regards the koala as the most typical of the marsupials, having the greatest number of the modifications peculiar to the order, and the smallest number of those common to other groups of mammals.
His classification of the order is into: 1, sarcophaga (flesh eaters), like dasyurus; 2, entomophaga (insect eaters), like the opossums; 3, carpophaga (fruit eaters), like the phalangers; 4, poephaga (plant eaters), like the kangaroos; and 5, rhizophaga (root eaters), like the wombat. - The first traces of mammals on the globe are the fossil remains of marsupials in the Stonesfield oolite and the gypsum (eocene) of Paris, so that at those epochs Europe was inhabited by animals of a type now confined to Australia and America; similar fossils have been found in the caverns of Wellington valley, New South Wales, and in the calcareous caverns of Brazil by Dr. Lund, very nearly allied to species now living in those countries.