Infraclass Eutheria belongs to one of the three infraclasses of the subclass Theria. Often the eutherians are referred to as placental mammals, placentals or higher mammals.
This infraclass has the following characteristics:
The young of the viviparous eutherians are born in an advanced stage of development. This is the result of an efficient nutritive connection between mother and embryo. The embryos are nourished by a placenta in which the membranes of the chorion and allantois play an essential part in carrying food materials and oxygen to the embryo and wastes and carbon dioxide back to the mother's blood stream. This is established by the fingerlike villi, which project from the embryonic portion of the placenta into the uterine portion.
Eutherian females have a single vagina of which the two uteri can be unfused to form duplex uteri (found in marsupials, in many rodents and bats) or to form a bipartite uterus or distally fused to form a bicornuate uterus, or even completely fused as in the higher mammals to form a simplex uterus.
A marsupial pouch is never present.
The penis is not bifurcated, and in most eutherian males a baculum is present. Normally a scrotum is present. The scrotum is located posterior to the penis in all eutherians except the order Lagomorpha (rabbits, hares and pikas), in which it is located anterior to the penis.
The brain is usually of considerable size, and a corpus callosum, which functions to allow both hemispheres to share memory and learning, is present.
The angle of the lower jaw is not inflexed and the palate is imperforate. The jugal usually has no contribution to the formation of the mandibular fossa.
There is a high variability in the dentition of the eutherians. The dental formula of primitive eutherians is: incisors 3/3, canines 1/1, premolars 4/4, and molars 3/3, with a total of 44 teeth. The number of incisors is never more than 3/3, and frequently occur in equal numbers in the lower and upper jaws.
Eutherian mammals live on all continents, in all oceans, and on many oceanic islands. Seventeen extant Eutherian orders are recognized (Subclass Theria): Insectivora, divers group of small eutherian mammals; Dermoptera, Colugas or flying lemurs; Chiroptera, Bats; Primates, prosimians, tarsiers, monkeys, apes and man; Edentata, sloths, armadillos and anteaters; Pholidota, Pangolins or scaly anteaters; Mysticeta, baleen whales; Odontoceta, toothed whales; Carnivora, carnivores; Lagomorpha, rabbits, hares and pikas; Rodentia, rodents; Tubulidentata, aardvark; Proboscidea, elephants; Hyracoidea, hyraxes, conies or dassies; Sirenia, manatee, dugong and sea cow; Perissodactyla, odd-toed ungulates: horses, rhinoceroses and tapirs; Artiodactyla, even-toed or cloven-hoofed ungulates. Of these, the order Insectivora is an assemblage of divers animals and often split into two or more orders. The order Carnivora was long divided into two orders: the Carnivora, containing only the fissiped carnivores, and the Pinnipedia, containing the seals, sea lions, and walruses. Many scientists considered the orders Mysticeta and Odontoceta as suborders of the single whale order Cetacea.