Mammals are in the animal worldmorphological structure Highest, physiologicalfunctionThe most perfect animal.Compared with other animals, the most prominent feature of mammals isViviparityAnd its young are fed by the milk secreted by the mother.Mammals have relatively developed brains, so they can produce more complex behaviors than other animals, and can constantly change their own behaviors to adapt to changes in the external environment.
There are more than 4000 kinds of mammals in the world. Although they have been highly evolved, they still have many similarities: almost all mammals arewarm-blooded animalThe body temperature is basically constant, and the body is covered with hair to protect the body from cold and heat.
Although the nest of mammals is not as good asbirdsIt is exquisite, but has many patterns and varied locations.moleThe underground caverns of;Most squirrels build their nests in tree holes, butGrey SquirrelBuilt nests on top of treesBranchesRoom;femalePolar bearDig holes for nests in the snow;somemarine animalasSea Dogs、SealsGenerally, they do not live in water, but nest on the bank.
predation
Many mammals go out to hunt at dusk every day.Because the temperature rises during the day,Reptiles、insectSuch cold-blooded animals are not easy to catch because they are active. Mammals have different methods of hunting.Cheetahs often catch their prey at a high speed;giraffeWrap it with a smart tongueleaf, twigs, and then pull down the leaves with canine teeth;ChipmunksUse your paws to rotate the food so as to scrape off the loose parts of the food and find out the parts that are easy to bite.
reproduction
ViviparityFertilization in mammals takes place in the mother's body.ZygoteAfter many splits, it finally becomes a fetus.In placental mammals, the fertilized egg passes through the uterusumbilical cordAnd the placenta connected with the uterine wall to obtain nutrients.By supplying blood to the placenta, the mother provides food and oxygen for the fertilized egg and takes away the waste.The fetus grows in the womb until birth.
lactation
During the period of newborn, female mammals will useAutocrineThe milk is fed to the young bybreastSecretion.When the baby sucks, milk will flow out of the breast.Breastfeeding is important for young babies, because milk is not only rich inglucoseAnd fat, can accelerate the growth of young, and contain antibiotics, can help young resist disease.
Growth of cubs
Compared with other animals, mammals spend more time and energy on their young.Generally, mammals produce fewer cubs each time, and the cubs need a lot of care to grow smoothly.Most female mammals should not only feed their young to keep them clean, but also protect them and teach them how to survive until they can live independently.
paleontologistIt is believed that the caniodonts living in the Triassic are the direct ancestors of mammals.CanodontSmall to medium sizeCarnivorousA few monotreme animals can exceed 90cm in length.They have many similarities with mammals, for example, they all have several different types oftoothThe limbs are under the body and can run quickly.
Mammals from therodontsreptile, but it is not sure which typeTheriodont 。Because in therodontoids, the nature of progress and the nature of primitive interlace, very complex.Such as earlyTheropodsMany of its features are primitive, butTemporal foramenBut it has increased, and the mammalian toe form of 2-3-3-3 has appeared.Trident has many progressive properties, and can almost be put into mammals, but it still remainsreptileOnmandibleConnection mode, i.eArticular boneThe connection of one bone.Therefore, various speculations have been made about the ancestors of mammals, such as canine teethMammals, Bao's mammalsictidosauria , Tridentate.The consensus is that mammals are of multiple origins, that is, the vast majority of mammals (includingPlacenta(dominant) originated from canids, but in a wide range ofMesozoic mammalsThere are also some from other animal teeth.
sincelate jurassic Since then, mammals have begun to step onto naturehistorical stage。The earliest mammal fossils were found in ChinaHadrocodium wui （Hadrocodium wui）, which lived 200 million years agojurassic period。ConghuaFrom the stone, the most important difference between mammals (especially early mammals) and reptiles is their teeth.Every reptiletoothThey are all the same. They are not different from each other. Mammalian teeth differentiate into different shapes according to their different positions on the jaw,ZoologistDifferent kinds of animals can be identified through the arrangement (dentition) of various tooth types.In addition, reptiletoothThe teeth of mammals are no longer renewed except for deciduous teeth.stayAnimal kingdomOnly mammals have three bones in their ears.They are two pieces of reptilesJawboneIt evolved.Up to the Tertiary, all mammals were very small.stayDinosaur extinctionPost mammals occupy manyNiche。By the Quaternary, mammals had become land occupationdominanceOf animals.[1]
Mammals have many unique characteristics, which greatly improves theSurvival rate, enhancednatural environmentOfadaptability，The most important features are:Further development of intelligence and sensory ability;Keep constant temperature；The improvement of reproduction efficiency;Get foodAnd the ability to handle food;There are hairs on the body surface, which are viviparous, and generally divided into five parts: head, neck, trunk, limbs and tail;Breathe with the lungs;Constant body temperature, YesThermostatic animal；The brain is large and developed.Lactation andViviparityIt is the most prominent feature of mammals.The embryo develops in the mother, and the mother gives birth to the fetus directly.Both parentbreastIt can secrete milk to feed the fetus.All these involve changes in the structure of various parts of the body, includingBrain volumeIncrease andNeocortexThe appearance of the sense of sight and smell is highly developed, and the sense of hearing is better than othersvertebrateGreater specialization;toothanddigestive systemThe specialization of food is conducive to the effective use of food;The specialization of limbs enhances the ability to move.Help to obtain food and escape from enemies;Breathingcirculatory systemThe perfect and unique fur covering the body surface helps to maintain its constant body temperature, thus ensuring that they canenvironment conditionTo survive.Viviparity, lactation and other unique characteristics, to ensure a higher survival rate of their offspring and the complexity of some speciesCommunity behaviorDevelopment of.
Another characteristic of mammals is that they havebreast(male or female), in which the mammary glands of female mammals are highly developed.In distinguishing between male and female mammalsSweat gland, hairmiddle earAuditory ossicleAnd the brainNeocortexTo make a difference.Except fiveMonoporeAll mammals produce offspring directly, except for about 50% of mammals.Most mammals have specialized adaptationsLiving conditionsTeeth.Mammals regulate body temperature andcirculatory system(including the heart).
Constant body temperature
Skin and hair are mammalianProtective layerThey can block the wind, rain and cold.Therefore, no matter how cold the weather is, mammals can rely on them to keep their body temperature constant to adapt to various complexClimatic environment。
brain
Mammals have larger brains than other vertebrates, and can better control their own thinkingprimate(e.gmonkey, orangutan).Mammals have more complex behaviors than other animals because of their developed brains.They will learn and can constantly change their behavior to adapt to changes in the external environment.
Keep clean
Mammalian hair is easy to hide dirt and becomeparasiteOfhotbed。Therefore, mammals have formed the habit of keeping clean to prevent disease transmission.They are kept clean in a variety of ways, such as licking, scratching, shaking, rolling, bathing, rubbing, gently biting, etc.
Body structure
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Skeletal structure
Every mammal has a pairOccipital condyleIt is the skull and the first cervical vertebra that form a joint, so that you can move more freely.The secondary oral bone hard jaw isolates the nasal cavity from the oral cavity. When breathing air, the gas will not enter the oral cavity, enabling mammals to breathe air while chewing food.In addition, the ribs of the mammalian neck heal on the cervical vertebra and become a part of the cervical vertebra.
Most mammals have ears that grow outside and can make sounds enter the brain directly, such as the funnel shape of catsauricleIt can guide sound waves into the inner ear so that cats can quickly capture sound and judgesound sourceDirection of.InsteadCanidaeMany mammals represented by animals can erect their ears and turn to the direction of sound in order to better capture sound.
nose
Mucosa at the back of the nose in many mammalsMuch greater thanAnthropogenicNasal mucosaTherefore, the sense of smell is more developed than that of humans.Sometimes, mice caught by people will spillUrinate, warn your companions to escape quickly with smell;Africa lionAvailableOlfactory traceIndicating the territory of its population;Trained pigs can smell undergroundTruffle。
tongue
The tongue of mammals is very developed and can move flexibly in the mouth.For example, deer, cattle, etcHerbivoresIts tongue can roll the fodder into the mouth freely;Tigerlionetc.CarnivoreCan lick water into the mouth with tongue;In hot summer or after running violently, dogs tend to stretch out their tongues and use them to dissipate heat in their bodies.
Mammalian teeth include incisors, caninesAnterior molarsDifferent from molars in shape and function.In addition, the tooth morphology of mammals is further specialized due to differences in food habits, such asCarnivoreIts canine teeth are developed, and its premolar and molar teeth are sharp, which is conducive to tearing and cutting food;The incisors and molars of herbivores are developed to break and grind the slender and soft plants.
tail
The tail of a mammal is an extension of its spine.The tails of different kinds of mammals are different in size, shape and function.Horsetail is thick and long, which can drive away mosquitoes, flies and insects;The fox's tail is covered with thick hair, which has a good heat preservation effect;BeaverTheir tails are used when they swimRudder。Sometimes, some mammals can also use their tails for defense.
Main categories
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Mammals belong toAnimal kingdom，Chordate，Vertebrate，Mammalia。The industry estimates that there are 5400 species of mammals, which are divided into about 1200 genera, 153 families and 29 orders.Mammals are divided into 2Subclass: Protomammalia (includingOogenesisOfMonoporeAnimals)Fauna(contains placental mammals andEgg viviparityOfMarsupialAnimals).Most mammals (including the six largest orders) belong to placental mammals.The three largest items areRodentia、ChiropteraandSoricomorpha 。Rodents include rats, Chiroptera includes bats, and Shrews includeShrew、moleandRattus guttatus。The other three largest items areCarnivora(Dogs, cats, weasels, bearsSealsEtc.), whale cloverleaf（Ungulates、whale），Primates(including humans).Mammals are divided into three main categories according to the mode of reproductionLower Outline: Monotremes, marsupials, placental mammals.
Mammals are various and widely distributed, mainly according to shape, skull, teethAppendageIt is divided into three categories according to birth modeSubclass：Protozoa(including the following 1-3)Metazoa(including the following 4~9)Eucerata(including 10-28 below), there are more than 4000 kinds of 28 orders.
According to the data in the book Mammal Species of the World in 2005,MammaliaAbout 5676 (2008 version of IUCNred data book5488), distributed in 1229 genera, 153 families and 29 orders, accounting for aboutChordate10%, 0.4% of all species on the earth.Rodentia(mouseporcupine、beaver、capybaraEtc.)Chiroptera(Bats, etc.) andSoricomorpha （Shrew) is the order with the most species in mammals.
The body structure of mammals is complex and different from that of other groupsbrainStructure, thermostatic system andcirculatory system, have the ability to breastfeed for offspring, most of them belong toViviparity, with hair follicles andSweat glandAnd other common external characteristics.They have various shapes, as small as 30mm long with wingsConcave faced bat, as large as 33 meters longfishOfBlue whale。They have a good environmentadaptability, distributed in a wide range of areas from the ocean to the mountains, from the tropics to the polar regions.Humans are also members of mammals.
July 2022, USAUniversity of Illinois Ebana- University of Champaign biologist Kevin Johnson andCo authorTo mammals“LiceTree "genomeResearch shows that lice parasitized on mammals today can be traced back to the same ancestor parasitized on mammals before the extinction of non avian dinosaurs.The research results were published in Nature Ecology and Evolution on July 4.[2]
December 2022, JapanNagoya University The research team pointed out that the brainPreoptic areaEP3 ofneuronIt plays a key role in regulating mammalian body temperature.[3]
In April 2024, the research team of Peking University found through research that the neuronal cluster called "suprachiasmatic nucleus" (SCN for short) in the deep brain region of mammals can calculate time through the "collective decision-making" of many neurons, and the accuracy rate of time decoding can reach 99%.This achievement was published online in the international authoritative journal Cell Research.[4]
Species anatomy
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skin
Mammalian skin is dense and well structured, which has important protective effects and good antiWater permeability, control body temperature and acuteSensory function。In order to adapt to the changeable external conditions, its skin texture, color, smell, temperature, etcenvironment conditionCoordination.
breastbyMammalsThe unique gland can secrete richNutrientsTo feed the young.Mammary gland is a kind of compound gland composed of tubular gland and vesicular gland, usually opening at the protrudingpapillaOn.The nipple is divided into real nipple andPseudopapillaThere are two types: one or more ducts open out directly from the true nipple;PseudopapillaryMammary ductThe utility model is opened in the cavity at the base of the nipple, and then opened outwards through the nipple by the general pipe.The number of nipples varies with species, from 2 to 19, and is often related to the litter size.Lower mammalMonotremeWithout nipples, the milk secreted by the mammary gland flows out along the hair and the baby directly licks it.Mammals without lips, such as whales, have muscles in the mammary gland area that can automatically press milk into the mouth of young whales.
Another kind of skin gland isSweat glandIt is a tubular gland. Its main function is to evaporate heat and remove some metabolic wastes.Body surface moistureEvaporative heat dissipationSweating is an important way for mammals to regulate body temperature. Some species with underdeveloped sweat glands mainly rely on evaporation from the surface of the mouth, tongue and nose to dissipate heat.
sebaceous glandsIt is a vesicular gland, opening at the base of hair follicleWhole plasma secretory glandIts secretion is oily, has the function of lubricating hair and skin, and is also an important source of exogenous hormones.The odor gland is a derivative of sweat gland or sebaceous gland. Its main function is to mark the field, transmit information, and some also have the role of self-defense.There are dozens of odor glands, such as musk glandsAnal gland、Abdominal gland, lateral glandDorsal gland、Prepuce glandEtc.The appearance and development of odor glands are usually related to mammals' sense of smell as the main way of hunting, while vision as the main waypositionerThe olfactory and odor glands of.
2. Hair: It is a unique structure of mammalsCuticular keratosisThe product of.TrichomeHairdoandHairy rootform.Hair shaft is composed of cortex andmedullaComponent composition;Hair roots are inserted into hair folliclesCoatSheath, with bulbous endHairballIts base is made of dermisDermal papillaThere are abundant blood vessels in it, which can transport the nutrients necessary for hair growth.There are openings of sebaceous glands in hair follicles, which can secrete oil and lubricate hair and skin;At the base of hair folliclePili erector muscleAttaches and shrinks to make hair stand upright, which helpsThermoregulation。Hirsutemorphological structure , which can be divided into long, tough and with certain hair directionNeedlehair（Prickly hair）, soft and hairless hair, and special needle hairTentacle。The external coat of mammals often forms a coat, which is mainly used for heat insulation and heat preservation.Aquatic mammals are basically hairless, such as whales, with developedsubcutaneous fat To keep the body temperature constant.The hair is often worn and faded, and there are usually one or two periodic hair changes every year. Generally, the hair in summer is short and sparse, with extremely poor heat, and the hair in winter is long and dense, with good heat preservation performance.The hair color of terrestrial mammalsenvironmentThe color of the mammal in the lower layer of the forest or dense vegetation is usually dark, gray in the open area, and sandy yellow in the desert area.
3. Horn: It is the specialized product of the epidermis and dermis of the mammalian head.The epidermis produces horny horns, such as the horny sheath of cattle and sheep and the epidermal horn of rhinoceros, and the dermis forms bone horns, such as deer horn.The horns of mammals can be divided intoCave corner、Real angle、Pronghorn horn, long necked antler, epidermal horn, etc.
Cave corner, composed of bone core and horny sheath, which is commonly called horn and is born in pairsFrontal boneOn the other hand, there is a growing trend that they will not be replaced throughout their lives.The hole angle isBovidaeUnique.
platypus
Real angle, is the forked bone horn, without horn sheath.The new horn has tender skin on the bone core, commonly known as antler, such asDeer Antler。After the horn grows, the velvety skin gradually ages and falls off, and finally only the forked bone horns, such as antlers, are retained.The antlers fall off and grow again periodically every yearDeer FamilyAnimal characteristics.With the exception of a few bisexual horns such asreindeer, or without horns, such as musk deer and roe deer. Generally, only males have horns.Pronghorn hornIt is a kind of horn between the cave horn and deer horn.The bone heart does not bifurcate, but the horn sheath has a small fork. The forked horn sheath has fused hairs, and the hairy horn sheathReproductive periodAfter replacement, the bone core does not fall off.This horn is malePronghornThe female pronghorn has only a short horn heart and no horn sheath.
4. Claw, nail and hoof: they are all derivatives of the skin, referring to the deformation of the cuticle of the epidermis at the (toe) end, but their shapes and functions are different.The claw is possessed by most mammals, and the claw of the species engaged in digging activities is particularly developed.CarnivoreIts claws are all sharp, such ascatamountIts claw is sharp and can be retracted. It is an effective predator weapon.A, essentially a flat claw, isprimatesUnique.The hooves are thickened claws,UngulatesIt is especially developed and can be continuously increased to compensate for the wear part.
bones
giraffe
MammalianSkeletal systemDeveloped, with complete functions of support, protection and movement.Mainly byAxis boneandAppendage skeletonIt consists of two major parts.The main features of its structure and function are: the skull has great specialization, with two occipital ankles,mandibleBy singleOdontoid boneComposition, tooth profile;The spinal column has obvious zoning, solid and flexible structure, and 7 cervical vertebrae;Move the limbs down to the abdomen, and when they appear, press the body up with the knee to adapt to the rapid movement on land.
Axis bone
Including skull and spine（vertebra）、sternum(sternum) and rib (rib).
1. Skull: Due to the development of mammalian brain and senses and the production of oral chewingconfigurationBe big.Cranial cavityfromFrontal bone、Parietal bone, occipital boneSphenoid bone、Ethmoid bone、Squama bone、Tympanic boneThe occipital bone, sphenoid bone, ethmoid bone, etc. are all formed by the healing of most bone blocks. The reduction and healing of bone blocks make the skull hard and light, which is an obvious feature of mammals.The brain is located in the cranial cavityForamen magnum occipitalisIt is connected to the spinal cord.There is an occipital ankle joint and the first cervical vertebra joint on both sides of the foramen magnum.The orbit, nasal cavity and oral cavity of mammals are mainly composed ofLacrimal bone, bone observation, nasal boneNasal concha、Maxilla、Premaxillary bone, palatal bonePterygoid bone、Vomer bone、mandible、Hyoid boneEtc.The mandible is composed of a pair of mandibles (dental bones), which is a landmark feature of mammalian skulls. The back end of the mandible is jointed with the squamous bone.
2. Spine: consists of a series ofVertebraeComposition, which can be divided into cervical vertebrae（cervical)、thoracic vertebra(thercic), lumbar spine（lumbar）, sacrum andCoccygeal vertebra(caudal）Five parts.There are usually 7 cervical vertebrae, and only a few of them are 6 (such asManatee）Or 8-10 pieces (such asThree-toed sloth ）The vast majority of mammals, regardless of the length of the neck (such as giraffes andhedgehog）All of them have 7 cervical vertebrae.The first cervical scaleatlas, the second cervical scaleaxisThe atlas is annular, forming a pair in frontArticular surfaceJoint with occipital ankle joint, anterior end of axis vertebral bodyOdontoid processAtlanticVertebral foramen, allowing the head to turn flexibly.There are usually about 13 thoracic vertebrae, each of which is connected with the rib andribs and sternum Common compositionchest；The sternum is segmented. Bats with flying ability and those living in underground cavesmoleAnd other mammals, such asbirdsSimilarkeelprotuberance.There are 4-7 lumbar vertebrae.Sacrum3 to 5, and fused into one, which is articulated with the waist belt;LimblessCetaceansThe sacrum is not obvious.The number of coccygeal vertebrae varies greatly with the length of the tail, ranging from 3-150.
1. Shoulder belt:Scapula、coracoid 、clavicleComposition.The shoulder blade of the shoulder strap of terrestrial mammals is very developed, and the crow's peck bone degenerates into a protuberance on the shoulder blade.Most clavicles tend to degenerate, and some have no clavicles, such asOdd hoofed speciesandArtiodactyla。The clavicle is developed in the groups suitable for climbing, digging and flying.It can be seen that the development of the clavicle is closely related to the movement mode of the forelimb. The clavicle degenerates for the type of forelimb that moves forward and backward, and the clavicle is developed for the type of forelimb that moves left and right.
2. Belt: from the boneIschiumandPubic boneComposition.The joint between the ilium and the sacrum, the left and right ischia and pubisMidabdomenHealing to form a piece of marrow bone, forming a closed pelvis.The waistband of mammals is healed, strengthening the support for the hind limbsFirmness。
3. Forelimb bone and hind limb bone: its structure is generalTerrestrial vertebratesThe pattern of is similar, but the front and rear soles (metatarsals) and fingers (toes) of the feet vary greatly with different lifestyles. For example, bats are specialized into winged limbs, and whales areFlipper, odd hoofed and cloven hoofed are quick walking limbs.exceptCetaceans、Hymenoptera、ChiropteraAnd sectionMarsupialsIn addition, most mammalian species haveKneecap，Knee jointForward turning improves the ability of support and movement, which is different from other mammalsTerrestrial Characteristics of vertebrates.According to the different ways of terrestrial mammals walking on the ground, foot types can be divided intoplantigrade 、Phalangeal lineAnd hoof walking.Among them, hoof walking has the smallest contact with the ground, which is a foot type suitable for fast running.
muscle
mammal
MammalianMuscle systemAndReptilesBasically similar, butStructure and functionAre further improved.Main characteristics: the muscles of the limbs and trunk are highPlasticity。In order to adapt to their different ways of movement, different muscle models have emerged, such as hoofed and carnivorous animals that are adapted to fast running have strong limb muscles.
Skin muscleVery developed.The skin muscles of mammals can be divided into two groups: one isLipomembranous muscleIt can make the whole body or local skin tremble to expel mosquitoes and flies and shake off attached foreign objects.Lipid membrane muscle can also curl up the bodyBallingOr erect thorns to defend against enemies, such asDace carp、porcupineHedgehog.In mammals, the lipid membrane muscle degenerates only in the chest, shoulder andgroinOccasionally reserved.The other group of skin muscles is the neckphysiological sphincter, its surfaceLatissimus colliIt extends down the chin and face along the neck ventral surface to form facial muscles andEmotive muscle。The lower type of expressionless muscle in mammals,CarnivoreThere are expression muscles. The expression muscles of primates are well developed, while the expression muscles of human beings are the most developed, with about 30.There are complex lip muscles around the mouth, which play a very important role in sucking.In addition, distributed inCranial sideandZygomatic arch, mandibularTemporalis muscleAnd chewing muscles are strong, which is closely related to predation, defense and chewing in the mouth.
Septum muscleA muscle peculiar to mammalsTransverse positionOfVoluntary muscleThe visceral cavity is divided into the thoracic cavity and the abdominal cavity. The activity of the septal muscles helps to breathe.
digestive system
Mammaliandigestive systemincludeAlimentary canalandDigestive gland。The main characteristics in structure and function are that the digestive tube is highly differentiated, oral digestion occurs, and the digestive ability is significantly improved.Related to this is that the digestive glands are very developed.
Alimentary canal
Including mouth, pharynx, esophagus, stomach, small intestine, large intestine, anus, etc.
1. Oral cavity: Mammalian oral mastication and oral digestion have caused great changes in oral structure.There are fleshy lips, which are important organs for sucking milk, feeding, and assisting mastication, and are part of the articulation organs.herbivorousMammalian lips are particularly developed, and some upper lips havecleft lip, such as rabbits.To adapt to oral chewing activities, mammalsOral fissureIt shrinks, and the cheeks appear on the outside of the teeth on both sides. Some kinds of cheeks also develop pocket shaped structuresBuccal pouchUsed to store food, such as monkeys.The parietal wall of the mouth is composed of boneHard palateandsoft palateTo open the nasal cavity（Internal nostril）Separated from the oral cavity, the nasal passage is along the hard palate.The soft palate moves backward until it faces the throat,Posterior nostrilOpening atPharyngeal cavity。The palate is often lined with keratinocytes to prevent food slippage.The herbivorous and carnivorous species have developed horny ridges.There is a well-developed muscular tongue in the mouth, which is helpful for feeding, stirring and swallowing, and is an auxiliary organ for human voice.Taste buds are distributed on the tongue surfaceGustatory organ。Onset of upper and lower mandibleProfiled tooth, teeth byAlveolarGrowing out, mediumMedullary cavity, filled with connective tissue, blood vessels and nerves.Due to different shapes and functions of teeth, they can be divided into incisors to cut food, dogs to tear food, molars to bite, cut, press, grind food and other functions.In mammals, there are auricular glandsSubmandibular glandandSublingual glandWait for 3 pairssalivary glands, with a catheter opening in the mouth, which can secreteSalivary amylaseTo digest food in the mouth.In addition, some mammalsEvaporation loss, as a form of thermoregulation.Rabbit and deer have four pairs of salivary glands.
2. Pharynx: The pharynx structure of mammals is perfect, connecting the oral cavity in the front and the throat and esophagus in the back.becauseSecondary palateThe inner nostril also opens to the pharynx, so the pharynx is the digestive tube andrespiratory tractAt the intersection of.On both sides of the pharynxEustachian tube（Euclidean tube）The opening of the middle ear cavity can be adjusted for protectionTympanic membrane。Lymphatic glands (tonsils) are distributed around the pharynx.There is an operculum outside the throatcartilageIt is opened and closed to solve the contradiction between breathing and swallowing at the intersection of pharynx and larynx.
3. Esophagus: a slender tube immediately after the pharynx, connecting the stomach at the lower end.The esophagus is the passage through which food passes, without digestion.
4. Stomach: It is an important part of the digestive tract of mammals. Its shape often changes due to different feeding habits. Most mammals areMonogastric；HerbivorousMammals are called Fuwei, also known asRuminant stomach, generally composed of 4 rooms, namelyrumenHoneycomb stomach（Reticulum）、Omasum stomachandGlandular stomach（abomasum）。Only the glandular stomach is the stomach body, withGlandular epitheliumIt can secrete gastric juice. The other three gastric chambers are deformed esophagus.The herbivorous animals with regurgitation need to carry out many times during food digestionRumination, until the food is fully decomposed.
5. Small intestine: The small intestine of mammals is the longest part of the digestive tract, includingduodenum、jejunumandileum。The small intestine is highly differentiated, and its mucosa is rich in villi, blood vessels, lymph andChyle duct, strengthening theabsorption。
6. Large intestine: shorter than small intestine, no villi on mucosaMucous glandIt can secrete alkaline mucus to protect and lubricate the intestinal wall and facilitate the excretion of feces.The first blind branch at the beginning of the large intestine iscecumThere is a vermicular process at the end.Cecum in univentricular stomachHerbivoresParticularly developed, exceptwalrus、armadillo、Giant anteater、HyraxExcept for one pair of cecum, other mammals have only one cecum.The large intestine of mammals can be divided into colon and rectum, and the rectum directly opens from the anus（CloacaDisappeared), is a mammal andAmphibian, reptiles and birds.
Digestive gland
In addition to three pairs of salivary glands, there are liver andpancreas, secreted separatelybileandPancreatic juice, injected into the duodenum.In addition to secreting bile, the liver also has storageGlycogenRegulate blood sugar to make excessamino acidDeoxygenation forms urine and other compoundsToxic SubstancesConvert to non-toxic substances and synthesizePlasma proteinAnd other functions.
respiratory system
Mammalianrespiratory systemVery developed, especially inRespiratory efficiencySignificant improvements have been made in this regard.Air passes through external nostrils, nasal cavity, throattracheaAnd into the lungs.
nasal cavity
Mammalian nasal cavity can be divided into upper olfactory part and lower respiratory part.The upper end of the nasal cavity has developedTurbinate, there areOlfactory cell。In addition, there areParanasal sinus, enhancing the warming, wetting and filtering effect of the nasal cavity on the air.At the same time, it is also vocalResonator。It is generally an external nostril, but cetaceans are specialized asSpray hole, forSingle nostril。
throat
The structure of mammalian larynx is perfect.The larynx is the distended part of the front end of the trachea, which is both the breathing channel and theArticulatory organ。Laryngeal origincartilage, ligament, muscle and mucosa.Entrance scale of throatLaryngeal orificeThe operculum cartilage at the front edge of the throat wall abdomen can cover the throat mouth when swallowing, and food and water enter the esophagus through the operculum, which can prevent food and water from entering the trachea by mistake.At ordinary times, the throat opening is the door of the air inlet and outlet pipes.fromThyroidCartilaginous and cricoidLaryngeal cavityThe vocal cords formed by mucosal folds on the side wall in the middle areVocal organ, began to appear in tailless amphibians, but mammals are the most developed (only monotremes andMarsupialAbsence).
trachea
It is located on the ventral surface of the esophagus and bifurcates into a pair after entering the thoraxa bronchial tubeTo the lungs.The main structural feature of the trachea and bronchus is that the tube wall is supported by many cartilage rings whose backs are not connected, thus ensuring the smooth flow of air.Tracheal mucosaIt has ciliated epithelium and mucus glands, which can filter air. The mucus secreted by the mucus glands can stick to the dust particles in the inhaled air. The dust particles are moved to the throat under the promotion of cilia, and discharged through the nose or mouth.
Lung and thorax
The structure of mammalian lung is the most complex, which is composed of“Bronchial tree”BronchobranchedBlind endmeanAlveoli。The number of alveoli is very large, which greatly increases breathingSurface areaFor example, the total area of alveoli in sheep can reach 50~90m2, that in horse can reach 500m2, and that in human can reach 70m2, which is equivalent toBody surface area40 times, significantly increasedgas exchangeThe effect of.Elastic fibers are distributed between the alveoli, which can passively retract the lungs with the cooperation of breathing.
The chest cavity holds the lungsCoelom, which is unique to mammals. When breathing activities are in progress, the elastic mouth position of the lung makes the thorax negative pressure, thus making the pleuralParietal layerKeep close to the dirty layer.In addition, it is unique for mammals to separate the thoracic cavity from the abdominal cavityDiaphragmDuring exercise, the volume of thorax can be changed, and the rise and fall of ribs can expand or reduce the volume of thorax, so that the lungs of mammals can expand and retract passively to complete exhalation and inspiration.
circulatory system
Mammaliancirculatory systemIncluding blood, heart, blood vessels andlymphatic system。Its remarkable feature is that it is very prominent in maintaining rapid circulation to ensure that there is enough oxygen and nutrients to maintain a constant body temperature.With leftArcus arteriosus corporis。red blood cellNuclear free.
blood
Mammalian blood and othersvertebrateThe difference is that red blood cells have no nucleus and are in the shape of two concave oblate disks, onlyCamelidaeandCervidaeThe red blood cells of;The volume of red blood cells is smaller than that of other vertebrates. For example, the red blood cells of frogs have a long and short diameter of 22.8μmX15．8μm. 14.7 for pigeonsμmX6．5μm. 5.1 for cattleμmX5．1μm. 2.5 for musk deerμmX2．5μm；The number of red blood cells in mammals is also more than that in other vertebrates, such asMammals6 to 13 million.These features greatly increase its surface area and improve its ability to combine with oxygen.
heart
The mammalian heart is located in the middle left of the thoraxpericardiumThere is a small amount of liquid in the cavity, which can reduce the friction when the heart beats.The internal structure of the heart is basically the same as that of birds. It is also four cavity, completeDouble circulation(First appeared, mammals originated earlier than birds)veinal bloodDo not mix in the heart.right atrium、right ventricleComposed of pulmonary artery and veinPulmonary circulation。The walls of right atrium and ventricle are thin, storing venous blood, and there areTricuspid Valve。left atrium、Left ventricleComposed of body arteries and veinsSystemic circulation。The left atrium and ventricle wall are thick, with internal storageArterial blood, compartmentmitral valve。The function of all these valves is to ensure that the blood flows in one direction and prevent the blood from reflow.The blood supply to the heart muscle isCoronary circulationCompleted.
The lymphatic system of mammals is very developed, which may be related to the high pressure of blood vessels in arteries and veins,Tissue fluidIt is difficult to return to the heart directly via vein.lymph glandOriginating between tissue spaces, with a blind tipLymphatic capillariesSome tissue fluid enters the lymphatic capillaries by osmosis.The composition of tissue fluid entering the lymphatic capillaries is similar to that of plasma, butproteinLow content, no red blood cells andplatelet。The lymphatic capillaries converge into larger lymphatic vessels and then pass throughThoracic ductThe anterior great vein was injected back to the heart.soLymphOnly for one-way flow from tissue to vein to heart.There are valves in the lymphatic vessels to prevent lymphatic reflux.Lymphatic vessels play an important role in maintaining blood volume by assisting the return of tissue fluid.In addition, lymphatic vessels are also the main way of fat transportation. The lymphatic vessels of the small intestine (chyle ducts) carry fat through the thoracic duct into the anterior great vein and return to the heart.lymph glandSection is generatedlymphocyteIt has the function of blocking foreign bodies and protecting the body.Mammalian lymph nodes are extremely developed, which are distributed throughout the lymphatic system, especially in the neck, armpit, mouse streammesenteryAnd other parts are relatively concentrated.In addition, tonsils, spleen and thymus are alsoLymphoid organ。
excretory system
Mammalianexcretory systemWell structured, including kidneysureter, bladder and urethra.In addition, the skin is also unique to mammalsExcretory organ。The main function of the excretory system is toCellular metabolismThe waste discharged from the body and theinternal environmentRelatively stable.Kidney is the main excretory organ. Mammalian kidneys usually consist of a pair, located at the back of the abdominal cavity and on both sides of the spine.The kidney is bean shaped, and its inner edge is concaveHilum of kidneyIt is the entrance and exit of arteries, veins, nerves and ureters.The kidney consists of cortex and medulla.At the hilum of the kidney, the beginning of the ureter expands intoRenal pelvis。The cortex is in the outer layer of the kidney and consists of numerousRenal corpuscle、Renal tubuleAnd vascular composition.Each renal corpuscle and renal tubule form aNephronEach kidney has hundreds of thousands or even millions of nephrons, and the renal corpuscle is formed by the coiled capillariesglomerulusAnd double wallRenal vesicleform.The renal tubules from the renal capsule are long and thin and coiled, extending from the cortex to the medulla.Renal tubules converging into medullaManifold, many manifolds are also composed ofRenal papillaIt opens in the renal pelvis, from which urine flows into the bladder through the ureter, and then out of the body through the urethra.
The formation of urine includes glomerularFiltration, renal tubule to collecting ductReabsorptionandSecretory action。When blood flows through the glomerulusarteriolePipe diameterAfferent arterioleSmall, so the blood pressure in capillaries increases, so the water in plasma andproteinMost substances other thanCapillary wallAnd the wall of the renal capsule.Therefore, urine production is caused by high and low blood pressure filtration.Mammalian urine is produced byureaComposition, while othersAmnionIt is composed of uric acid.Urea is produced by the secretion of renal tubules and can thicken urine.
nervous system
Mammaliannervous systemHighly developed, mainly inbrainandcerebellumThe volume increases and developsNeocortexComplex folds (sulci and gyri) have been formed on the surface of the brain, greatly increasing the surface area of the new cortex.
Neocortex
Is created byLateral ventricleThe nerve substance on the outer wall grows and surrounds the primary cerebral cortex（Procephalum）The remnant of the protocortex is called the hippocampus, which is still the olfactory center in the lateral ventricle.Cerebral cortexIt is composed of developed neocortex, which receives variousSensory organThe impulses transmitted will be reflected according to the established neural connections through analysis and synthesis.aboutCerebral hemisphereThrough manynerve fiberContact each other.The pathway formed by nerve fibers is calledcorpus callosum, is a mammal（Placenta）Unique structure.
It is covered by the cerebral hemisphere and hasPineal glandThe pineal gland of mammals tends to shrink.From the ventral surface of diencephalonoptic nerve, forming cross scaleOptic chiasma, followed by a handlethe pituitaryConnect.Diencephalic cavityAlso known asThird ventricle, very developed.The neural structures in the diencephalon wall are mainly dorsalthalamusAlso known as the thalamus and ventralHypothalamus。The thalamus is the lower center and cerebral cortexanalyzerBetweenIntermediate station, sensory impulses from the whole body are concentrated hereCerebral gray matterReplace with another neuron and reenter the cerebral cortex.The ventral hypothalamus isAutonomic nerveThe activity center is closely related to the coordination of visceral activities and isThermoregulatory center。
The midbrain of mammals is underdeveloped and very small. The midbrain cavity is narrow and forms a tube, calledMidbrain aqueduct, and the thirdFourth ventricleTransportation.The dorsal midbrain hasQuadruplex, the front pair is visualReflex centerThe back pair is the auditory reflex center.The base of the midbrain is descendingmotor nerveFasciculusThe brain and foot constitute a significant part.
cerebellum
mammalHindbrainThe back ofMuscle movementAnd the balance center for maintaining the normal posture of the body.The unique structural feature of mammalian cerebellum isCerebellar cortex, whose ash is covered on the surface, formingCerebellar cortex，white matterIt is dendritic and deep into gray matter.In addition, in twoCerebellar hemisphereHorizontal betweenNerve fiber bundleConstitute mammalianPonsThe pons are the intermediate station of the communication pathway between cerebellum and brain.
Connected to the spinal cord, bothStructural similarity。The medulla has ascending and descending conduction pathways in the white matter in addition to the pathway connecting the spinal cord and the higher central nervous system.Grey matter is dispersed into someNucleus nervi, the nerve fibers of the nerve nucleus and the corresponding sensory andMotor organContact.The medulla is also an important center for visceral activities, which can regulate breathing, digestion, circulation, sweat gland secretion and variousDefensive reflex。There is a fourth ventricle on the back of the medulla.
Each part of mammalian brain emits 12 pairsCerebral nerve, respectively, the functions of sensation and movement.These 12 pairs of names, sending sites, distribution and main functions of brain nerves will be discussed later.MammalianAutonomic nervous systemIt is very developed. Its main function is to regulate visceral activities and metabolic processes, and maintain the bodyinternal environmentBalance of.The autonomic nervous system can be divided intoSympathetic nervous systemandParasympathetic nervous system。sympathetic nerveThe system includes nerve fibers originating from the thoracolumbar segment of the spinal cord and distributed to the internal organs through the sympathetic nerve chain.parasympatheticThe system consists of part of the brain nervesOculomotor nerve、facial nerve、Glossopharyngeal nerve、vagusIt is composed of nerves originating from the sacrum of the spinal cord.The effects of sympathetic and parasympathetic nerves on visceral organs are antagonistic, that is, most visceral organs are doubly innervated by sympathetic and parasympathetic nerves, such as stimulationCardiac sympathetic nerveAccelerate the heart beat, and stimulate the vagus nerve (parasympathetic) to slow the heart beat.
intelligence
The mammalian nervous system is highly developed, especially the brain becomes more complex. The new brain cortex emerging from reptiles is highly developed by mammals, formingAdvanced nervous activitythe central administration.neuronThe number increased greatly, and the transverse nerve fibers, namely the corpus callosum, were connected between the two cerebral hemispheres.Moreover, the cerebellum is developed, and the cerebellar hemisphere appears for the first time.The unprecedented development of mammalian cerebral cortex provides a necessary basis for operation and logic.This is not available to all animals before mammals.Therefore, the intelligence of mammals is higher than that of other non mammals.
sensory organs
Mammals rely on highly developed senses to find food, avoid enemies, and find suitable habitat. At the same time, it is also a communication link between species and a series of behavioral reactionsIndivisibleOrgans of.Of course, not all group senses have reached a high level of development. Some species are in a state of degeneration in many aspects, while in one aspect they are highly specialized.For example, some kinds of mammals with vision deterioration have also developed special high and low frequency acoustic pulse systems when they are moving fastechoTo locate, bats use high-frequency sound wavesEcholocation，dolphinHigh frequency and low frequency acoustic echo are used for positioning.This isbionicsThe research is of great significance.
The senses of mammals are highly developed, mainly reflected in theirPerfect visual, auditory and olfactory structures.
smell
Most mammals have an enlarged nasal cavity and developed nasal concha bone, and are sensitive to smell.Such as eating meat, cloven hooves andRodentThe sense of smell is quite developed.But the sense of smell of whales and primates is not developed, so their sense of smell is not sensitive. Dolphins andPorpoiseIs lackingOlfactory organ。
vision
MammalianVisual organSimilar to most amniotic animals.Most mammals have well-developed eyeballs.But some of them live undergroundInsectivoresThe eyeballs of rodents and cetaceans are extremely degenerated, and even some species only maintain the ability to distinguish between light and dark.In general, mammals are sensitive to light waves, butColor visionIs poor, which is different from mostMammalsAll are related to night activities.Primates are more accurate in color discrimination and in judging the size and distance of objects.
endocrine system
Mammalianendocrine systemExtremely developed.It consists of endocrine glands scattered throughout the body, including the brainthe pituitary, thyroidParathyroid gland、adrenal glandIslet gland, thymus gland and gonad.The different hormones they secrete have different functions and are related to each other to form an endocrine system.
The male gonad of mammals is a pair of testes, and its position often varies with species.Most kinds of testiclesBreeding periodThere is displacement or falling phenomenon.exceptMonoporeAnimal elephantrhinocerosThe testis of most mammals will drop from the abdominal cavity to the scrotum outside the abdominal cavity through the groin during the embryo.Testicular displacement can be classified into three types: ① abdominal testicle.The testis does not change position, and is located behind the kidney, such as monotremesLong Nose、Pyrola, Manatees andInsectivoraAnimals of some families. ②Inguinal testis.The testicles move into the groin, asErinaceae、Lepidoptera、Tracheodonta、Sealidae、TapiridaeandMicrobats。③Scrotal testis.The testicle moves into a scrotum that is pendulous or not, such asRuminant、PrimatesAnd most marsupials are suspensory scrotum;Rodentia, AnamorphaCarnivora、Equidae、Swine family、Sea DogsSectionMegabatsThe scrotum is not hanging.
It is a pair of ovaries, and its surface layer isGenital epithelium, which is produced by the reproductive epithelium and is in different development stagesFollicles, each follicle contains oneEgg cell, with follicular fluid outside, containingestrogen, mature follicles rupture, eggs andovarian follicleThe liquid is discharged.Other residual follicles atrophy and are filled with a yellow cellCorpus luteum, can secrete hormones, promote the uterus andbreastDevelopment, preparing for pregnancy.After the mature eggs are discharged, they enter the opening in the front of the fallopian tube. After fertilization is completed in the upper part of the fallopian tube, they reach the uterus along the fallopian tube, and the fertilized eggs are planted on the uterine wall for development.The uterus opens outside the body through vagina.There are many types of mammalian uterus, some of which are primitiveDouble uterus, such asLagomorpha, Rodentia and Hyalus;Some are bisected uterus, such as cetaceans;Some areBicornical uterus, such as Insectivora, Lepidoptera, Carnivora, Manatee, Long NoseOdaria、Artiodactyla, some species of Chiroptera and Primate;Another one is for two uterus to completely heal into oneSingle uterus, such as some species of Chiroptera and Primate.The development of these different types of uterus is from the original twin uterus to the single uterus.The number of babies born in a single uterus is usually less than that in a double uterus
