Mammals

MAMMALS (Mammalia), or beasts, form a class belonging to the subphylum of vertebrates (Vertebrata) and the phylum of chordates (Chordata). M. are particularly characterized by a hairy covering and skin mammary glands, the secretion of which—milk—is used for feeding the young. Warm-blooded M. are typical terrestrial animals; some species have adapted to life in trees, in the ground, or in water. The most typical appearance is that of terrestrial M. with a clear division of the body into head, neck, trunk, and tail. There are 4 limbs; the hind pair in some aquatic M. (whales) is reduced. Hairs are keratinized appendages of the skin, serving to protect the body from cooling, as well as organs of touch. They may be reduced or reach great length (horse's tail), thickness (bristles), and hardness (quills). Skin glands include sebaceous and sweat glands. They are not present in all M. Other keratinized appendages of the M. coverings are scales (beaver's tail, pangolin scales), claws, hooves, nails, and the horny sheath of hollow horns. The M. skeleton is an internal ossifying skeleton; in a few species there is an external skeleton (armadillo). Typically there are 7 cervical vertebrae, 12-24 dorsal, 5-7 lumbar, 2-9 sacral, and 3-46 caudal. There are true and false ribs in varying numbers. The sternum is characteristic of all M. The skull has 2 occipital condyles. The quadrate bone enters the tympanic cavity, where it transforms into the auditory ossicle (incus). The gill skeleton remains in the form of the hyoid bone and laryngeal cartilages. In many M* the pectoral girdle consists only of the shoulder blades. The typical number of fingers in a limb is 5; it may be reduced to 1. Teeth are set in sockets. Incisors, canines, and molars are distinguished. Some types of teeth may be reduced; rarely are there no teeth at all (echidna, anteater). Teeth are usually replaced once. The stomach is simple in ruminants it is complex, consisting of the rumen, reticulum, omasum, and abomasum. From the reticulum, food is regurgitated into the mouth, is chewed a second time, and then passes to the omasum and abomasum. The rectum opens into the anus, while in monotremes it opens into the cloaca. The heart is four-chambered; the aortic arch curves to the left. The lungs are of a toothed structure with a very large surface area of alveoli. The kidneys are secondary. They are of separate sexes. The uterus is double, bipartite, bicornuate, or simple—ordinary. The oviducts open with funnels into the body cavity and do not fuse with the ovaries. The uterus passes into the vagina. There are female external genital organs (labia, clitoris, in some cases—hymen). In males, the sexual apparatus is connected with excretory organs; it consists of testes, vasa deferentia, seminal vesicles, accessory glands, and a copulatory organ penetrated by a canal that expels both urine and semen. Lower M. are egg-laying, the rest are viviparous. Fertilization is internal. The embryo is enveloped in membranes. The eggs of viviparous M. are very poor in nutritive yolk. The nourishment of the embryo in viviparous M. is provided by the maternal organism through the intermediary of the fetal place, or placenta, the form and structure of which vary (non-deciduous or deciduous placenta, in the latter case—diffuse, zonary, cotyledonary, discoidal).-The cerebral hemispheres are strongly developed in the main brain, with many M. having convolutions; the hemispheres cover other parts of the brain (in humans including the cerebellum). There are 12 pairs of cranial nerves. The significance of M. for humans is diverse and great. Many of them serve as food (meat, fat, lard, milk, blood); internal secretion glands are used for preparing medicinal extracts and for extracting hormones. In pharmacy, fat, lard, lanolin, and spermaceti (sperm whale) have auxiliary value. Castoreum and musk are still medicinal substances, though rarely used. Blood in liquid form and raw liver are used for dietary treatment. Catgut is prepared from sheep intestines. Various types of skin are used for making prostheses. Pieces of bone are used in plastic operations. The testes of monkeys and other M., as well as the parathyroid glands, can be transplanted to humans for therapeutic purposes. Some M. (horse) are used for preparing therapeutic and preventive sera. Other M. are indispensable laboratory animals (see).-The harm from M. to humans is in turn diverse. Humans can contract various diseases from wild and domestic M. (see Zoonoses). The role of M. as intermediate hosts of parasitic worms of humans is important. Many M. are very important economically as agricultural pests (see Rodents). Classification of M. Orders: 1. Monotremata. Egg-laying M.—platypus, echidna (Australia). 2. Marsupialia with a abdominal pouch for "carrying" born underdeveloped embryos—kangaroo, bandicoot, etc. 3. Insectivora—hedgehogs (beneficial animal), shrews, moles. 4. Chiroptera, or bats. The anterior limb is a thin long one covered with a skin membrane forming the flying apparatus—pipistrelle, noctule, and others. They feed on insects. They can play a role as mosquito destroyers. 5. Edentata—armadillos, sloths, anteaters, pangolin (South America, partly the Old World). 6. Rodentia. 7. Carnivora; canines are well developed; molars are sharp-cusped or with blunted cusps. True carnivores lead a terrestrial way of life: family Felidae—cat, lion, tiger, etc.; family Viverridae with genera Viverra: (they produce a substance viverreum, similar to musk and secreted by skin glands of the genital area), Herpestes (mongoose—immune to snake venom); family Canidae—dog, fox, wolf; family of bears, raccoons, martens, etc. (commercial animals). Aquatic carnivores are Pinnipedia: seals, walruses, etc. 8. Cetacea with toothed whales (dolphin, sperm whale, narwhal) and toothless whales equipped with horny plates hanging from the palate (baleen of whales)—commercial¹ animals—Greenland whale, right whale, etc. 9, 10. Ungulata with suborders: even-toed ungulates (Artiodactyla)—family Suidae, Camelidae, Bovidae, Cervidae and others; odd-toed ungulates (Perissodactyla)—family Tapiridae, Rhinocerotidae and Equidae. In addition to ungulates, the family Elephantidae, sirenians and others belong here. 11. Primates; family of prosimians (Lemuridae) and group of families of anthropoids (Anthropomorpha) - flat-nosed monkeys (Platyrrhina); families of marmosets (Hapalidae) and howler monkeys (Cebidae); narrow-nosed (Catarrhina); families of monkeys (Cercopithecidae), gibbons (Hylobatidae), apes (gorilla, orangutan, chimpanzee) and human [Hominidae (Homoprimigenius, H. sapiens)].