Structure and functions of the animal skeleton. Nervous system and sensory organs of vertebrates. Vertebrate skin

In the process of evolution, animals mastered more and more new territories, types of food, and adapted to changing living conditions. Evolution gradually changed the appearance of animals. In order to survive, it was necessary to search for food more actively, hide better or defend against enemies, and move faster. Changing with the body, musculoskeletal system had to provide all these evolutionary changes. The most primitive protozoa have no supporting structures, move slowly, flowing with the help of pseudopods and constantly changing shape.

The first support structure to appear is cell membrane. She not only separated the body from external environment, but also made it possible to increase the speed of movement due to flagella and cilia. Multicellular animals have a wide variety of support structures and devices for movement. Appearance exoskeleton increased the speed of movement due to the development of specialized muscle groups. Internal skeleton grows with the animal and allows it to reach record speeds. All chordates have an internal skeleton. Despite significant differences in the structure of musculoskeletal structures in different animals, their skeletons perform similar functions: support, protection internal organs, body movement in space. The movements of vertebrates are carried out due to the muscles of the limbs, which carry out such types of movement as running, jumping, swimming, flying, climbing, etc.

Skeleton and muscles

The musculoskeletal system is represented by bones, muscles, tendons, ligaments and other connective tissue elements. The skeleton determines the shape of the body and, together with the muscles, protects the internal organs from all kinds of damage. Thanks to joints, bones can move relative to each other. The movement of bones occurs as a result of contraction of the muscles that are attached to them. In this case, the skeleton is a passive part of the motor apparatus that performs a mechanical function. The skeleton consists of dense tissues and protects internal organs and the brain, forming natural bone containers for them.

In addition to mechanical functions, the skeletal system performs a number of biological functions. Bones contain the main supply of minerals that are used by the body as needed. Bones contain red bone marrow, which produces shaped elements blood.

The human skeleton includes a total of 206 bones - 85 paired and 36 unpaired.

Bone structure

Chemical composition of bones

All bones consist of organic and inorganic (mineral) substances and water, the mass of which reaches 20% of the mass of the bones. Organic matter of bones - ossein- has elastic properties and gives elasticity to bones. Minerals - salts of carbon dioxide and calcium phosphate - give bones hardness. High bone strength is ensured by a combination of ossein elasticity and hardness mineral matter bone tissue.

Macroscopic bone structure

On the outside, all bones are covered with a thin and dense film of connective tissue - periosteum. Only the heads of long bones do not have periosteum, but they are covered with cartilage. The periosteum contains many blood vessels and nerves. It provides nutrition to bone tissue and takes part in the growth of bone thickness. Thanks to the periosteum, broken bones heal.

Different bones have different structures. A long bone looks like a tube, the walls of which consist of a dense substance. This tubular structure long bones gives them strength and lightness. In the cavities of the tubular bones there is yellow bone marrow - rich in fat loose connective tissue.

The ends of the long bones contain cancellous bone substance. It also consists of bony plates that form many intersecting septa. In places where the bone is subject to the greatest mechanical load, the number of these partitions is highest. The spongy substance contains red bone marrow, the cells of which give rise to blood cells. Short and flat bones also have a spongy structure, only on the outside they are covered with a layer of damlike substance. The spongy structure gives bones strength and lightness.

Microscopic structure of bone

Bone tissue belongs to the connective tissue and has a lot of intercellular substance, consisting of ossein and mineral salts.

This substance forms bone plates arranged concentrically around microscopic tubules that run along the bone and contain blood vessels and nerves. Bone cells, and therefore bone, are living tissue; She gets nutrients with blood, metabolism occurs in it and structural changes can occur.

Types of bones

The structure of bones is determined by the process of long historical development, during which the body of our ancestors changed under the influence of the environment and adapted through natural selection to the conditions of existence.

Depending on the shape, there are tubular, spongy, flat and mixed bones.

Tubular bones are located in organs that make rapid and extensive movements. Among the tubular bones there are long bones (humerus, femur) and short bones (phalanxes of the fingers).

Tubular bones have a middle part - the body and two ends - the heads. Inside the long tubular bones there is a cavity filled with yellow bone marrow. The tubular structure determines the bone strength required by the body while requiring the least amount of material. During the period of bone growth, between the body and the head of the tubular bones there is cartilage, due to which the bone grows in length.

Flat Bones They limit cavities within which organs are placed (skull bones) or serve as surfaces for muscle attachment (scapula). Flat bones, like short tubular bones, are predominantly composed of spongy substance. The ends of long tubular bones, as well as short tubular and flat bones, do not have cavities.

Spongy bones built primarily of spongy substance covered with a thin layer of compact. Among them, there are long spongy bones (sternum, ribs) and short ones (vertebrae, carpus, tarsus).

TO mixed bones These include bones that are made up of several parts that have different structures and functions (temporal bone).

Protrusions, ridges, and roughness on the bone are places where muscles are attached to the bones. The better they are expressed, the more developed the muscles attached to the bones are.

Human skeleton.

The human skeleton and most mammals have the same type of structure, consisting of the same sections and bones. But man differs from all animals in his ability to work and intelligence. This left a significant imprint on the structure of the skeleton. In particular, the volume of the human cranial cavity is much larger than that of any animal that has a body of the same size. The size of the facial part of the human skull is smaller than the brain, but in animals, on the contrary, it is much larger. This is due to the fact that in animals the jaws are an organ of defense and acquisition of food and are therefore well developed, and the volume of the brain is less than in humans.

Curvatures of the spine associated with a shift in the center of gravity due to vertical position body, help a person maintain balance and soften shocks. Animals do not have such bends.

The human chest is compressed from front to back and close to the spine. In animals it is compressed from the sides and extended towards the bottom.

The wide and massive human pelvic girdle has the shape of a bowl and supports the organs abdominal cavity and transfers body weight to the lower limbs. In animals, body weight is evenly distributed between the four limbs and the pelvic girdle is long and narrow.

The bones of the lower limbs of humans are noticeably thicker than the upper ones. In animals there is no significant difference in the structure of the bones of the fore and hind limbs. Greater mobility of the forelimbs, especially the fingers, allows a person to perform a variety of movements and types of work with his hands.

Skeleton of the torso axial skeleton

Skeleton of the torso includes a spine consisting of five sections, and the thoracic vertebrae, ribs and sternum form chest(see table).

Scull

The skull is divided into the brain and facial sections. IN brain The section of the skull - the cranium - contains the brain, it protects the brain from blows, etc. The skull consists of fixedly connected flat bones: the frontal, two parietals, two temporal, occipital and sphenoid. The occipital bone is connected to the first vertebra of the spine using an ellipsoidal joint, which allows the head to tilt forward and to the side. The head rotates along with the first cervical vertebra due to the connection between the first and second cervical vertebrae. There is a hole in the occipital bone through which the brain connects to the spinal cord. The floor of the skull is formed by the main bone with numerous openings for nerves and blood vessels.

Facial the skull section forms six paired bones - the upper jaw, zygomatic, nasal, palatine, inferior nasal concha, as well as three unpaired bones - the lower jaw, vomer and hyoid bone. The mandibular bone is the only bone of the skull that is movably connected to the temporal bones. All bones of the skull (except lower jaw), are connected motionlessly, which is due to the protective function.

The structure of the human facial skull is determined by the process of “humanization” of the monkey, i.e. the leading role of labor, the partial transfer of grasping function from the jaws to the hands, which have become organs of labor, the development of articulate speech, the consumption of artificially prepared food, which facilitates the work of the masticatory apparatus. The cranium develops in parallel with the development of the brain and sensory organs. Due to the increase in brain volume, the volume of the cranium has increased: in humans it is about 1500 cm 2.

Skeleton of the torso

The skeleton of the body consists of the spine and chest. Spine- the basis of the skeleton. It consists of 33–34 vertebrae, between which there are cartilage pads - discs, which gives the spine flexibility.

The human spinal column forms four curves. In the cervical and lumbar spine they are convexly facing forward, in the thoracic and sacral spine - backward. IN individual development In humans, curves appear gradually; in a newborn, the spine is almost straight. First, the cervical curve forms (when the child begins to hold his head straight), then the thoracic curve (when the child begins to sit). The appearance of lumbar and sacral curves is associated with maintaining balance in an upright position of the body (when the child begins to stand and walk). These bends have an important physiological significance- increase the size of the thoracic and pelvic cavities; make it easier for the body to maintain balance; soften shocks when walking, jumping, running.

With the help of intervertebral cartilage and ligaments, the spine forms a flexible and elastic column with mobility. It is not the same in different parts of the spine. The cervical and lumbar spine have greater mobility; the thoracic spine is less mobile, as it is connected to the ribs. The sacrum is completely motionless.

There are five sections in the spine (see diagram “Divisions of the spine”). The size of the vertebral bodies increases from the cervical to the lumbar due to greater load to the underlying vertebrae. Each vertebrae consists of a body, a bony arch and several processes to which muscles are attached. There is an opening between the vertebral body and the arch. The foramina of all vertebrae form spinal canal where the spinal cord is located.

Rib cage formed by the sternum, twelve pairs of ribs and thoracic vertebrae. It serves as a container for important internal organs: heart, lungs, trachea, esophagus, large vessels and nerves. Takes part in breathing movements due to the rhythmic rise and fall of the ribs.

In humans, in connection with the transition to upright walking, the hand is freed from the function of movement and becomes an organ of labor, as a result of which the chest experiences a pull from the attached muscles of the upper limbs; the insides do not press on the front wall, but on the lower one, formed by the diaphragm. This causes the chest to become flat and wide.

Skeleton of the upper limb

Skeleton of the upper limbs consists of the shoulder girdle (scapula and collarbone) and free upper limb. The scapula is a flat, triangular bone adjacent to the back surface chest. The collarbone has a curved shape, resembling Latin letter S. Its significance in the human body is that it leaves shoulder joint at some distance from the chest, providing greater freedom of movement of the limb.

The bones of the free upper limb include the humerus, the bones of the forearm (radius and ulna) and the bones of the hand (bones of the wrist, bones of the metacarpus and phalanges of the fingers).

The forearm is represented by two bones - the ulna and the radius. Due to this, it is capable of not only flexion and extension, but also pronation - turning inward and outward. The ulna at the top of the forearm has a notch that connects to the trochlea of ​​the humerus. The radius bone connects to the head of the humerus. In the lower part, the radius has the most massive end. It is she who, with the help of the articular surface, together with the bones of the wrist, takes part in the formation of the wrist joint. On the contrary, the end of the ulna here is thin, it has a lateral articular surface, with the help of which it connects to the radius and can rotate around it.

The hand is the distal part of the upper limb, the skeleton of which is made up of the bones of the wrist, metacarpus and phalanges. The wrist consists of eight short spongy bones, arranged in two rows, four in each row.

Skeleton hand

Hand- the upper or forelimb of humans and monkeys, for which the ability to oppose the thumb to all the others was previously considered a characteristic feature.

The anatomical structure of the hand is quite simple. The arm is attached to the body through the bones of the shoulder girdle, joints and muscles. Consists of 3 parts: shoulder, forearm and hand. The shoulder girdle is the most powerful. Bending your arms at the elbow gives your arms greater mobility, increasing their amplitude and functionality. The hand consists of many movable joints, it is thanks to them that a person can click on the keyboard of a computer or mobile phone, point a finger in the desired direction, carry a bag, draw, etc.

The shoulders and hands are connected through the humerus, ulna and radius. All three bones are connected to each other using joints. At the elbow joint, the arm can be bent and extended. Both bones of the forearm are connected movably, so during movement in the joints, the radius rotates around the ulna. The brush can be rotated 180 degrees.

Skeleton of the lower limbs

Skeleton of the lower limb consists of the pelvic girdle and the free lower limb. The pelvic girdle consists of two pelvic bones, articulated posteriorly with the sacrum. The pelvic bone is formed by the fusion of three bones: the ilium, the ischium and the pubis. Complex structure This bone is determined by a number of functions it performs. Connecting to the thigh and sacrum, transferring the weight of the body to the lower limbs, it performs the function of movement and support, as well as protective function. Due to the vertical position of the human body, the pelvic skeleton is relatively wider and more massive than that of animals, since it supports the organs lying above it.

The bones of the free lower limb include the femur, tibia (tibia and fibula) and foot.

The skeleton of the foot is formed by the bones of the tarsus, metatarsus and phalanges of the fingers. The human foot differs from the animal foot in its arched shape. The arch softens the shocks the body receives when walking. The toes in the foot are poorly developed, with the exception of the big one, as it has lost its grasping function. The tarsus, on the contrary, is highly developed, especially large in it calcaneus. All these features of the foot are closely related to the vertical position human body.

Human upright walking has led to the fact that the difference in the structure of the upper and lower limbs has become significantly greater. Human legs are much longer than arms, and their bones are more massive.

Bone connections

There are three types of bone connections in the human skeleton: fixed, semi-movable and mobile. Fixed type of connection is a connection due to fusion of bones (pelvic bones) or the formation of sutures (skull bones). This fusion is an adaptation to bear the heavy load experienced by the human sacrum due to the vertical position of the torso.

Semi-movable the connection is made using cartilage. The vertebral bodies are connected to each other in this way, which contributes to the tilt of the spine in different directions; ribs with the sternum, which allows the chest to move during breathing.

Movable connection, or joint, is the most common and at the same time complex form of bone connection. The end of one of the bones that forms the joint is convex (the head of the joint), and the end of the other is concave (the glenoid cavity). The shape of the head and socket correspond to each other and the movements carried out in the joint.

Articular surface The articulating bones are covered with white shiny articular cartilage. Smooth surface articular cartilage facilitates movement, and their elasticity softens the shocks and shocks experienced by the joint. Typically, the articular surface of one bone forming a joint is convex and is called the head, while the other is concave and is called the socket. Thanks to this, the connecting bones fit tightly to each other.

Bursa stretched between the articulating bones, forming a hermetically sealed joint cavity. The joint capsule consists of two layers. The outer layer passes into the periosteum, the inner layer releases fluid into the joint cavity, which acts as a lubricant, ensuring free sliding of the articular surfaces.

Features of the human skeleton associated with work and upright posture

Labor activity

The body of a modern person is well adapted to work and walking upright. Upright walking is an adaptation to the most important feature of human life - work. It is he who draws a sharp line between man and higher animals. Labor had a direct impact on the structure and function of the hand, which began to influence the rest of the body. The initial development of upright walking and the emergence of labor activity entailed further changes in the entire human body. The leading role of labor was facilitated by the partial transfer of the grasping function from the jaws to the hands (which later became organs of labor), the development of human speech, and the consumption of artificially prepared food (facilitates the work of the masticatory apparatus). Brain department The skull develops in parallel with the development of the brain and sensory organs. In this regard, the volume of the cranium increases (in humans - 1,500 cm 3, in apes - 400–500 cm 3).

Upright walking

A significant part of the characteristics inherent in the human skeleton is associated with the development of bipedal gait:

• supporting foot with a highly developed, powerful big toe;
• hand with a very developed thumb;
• the shape of the spine with its four curves.

The shape of the spine was developed thanks to a springy adaptation to walking on two legs, which ensures smooth movements of the torso and protects it from damage during sudden movements and jumps. The body in the thoracic region is flattened, which leads to compression of the chest from front to back. The lower limbs also underwent changes in connection with upright walking - widely spaced hip joints give stability to the body. During evolution, a redistribution of body gravity occurred: the center of gravity moved down and took a position at the level of 2–3 sacral vertebrae. A person has a very wide pelvis, and his legs are widely spaced, this allows the body to be stable when moving and standing.

In addition to the curved spine, the five vertebrae of the sacrum, and the compressed chest, one can note the elongation of the scapula and the expanded pelvis. All this entailed:

• strong development of the pelvis in width;
• fastening the pelvis to the sacrum;
• powerful development and a special way to strengthen the muscles and ligaments in the hip area.

The transition of human ancestors to upright walking entailed the development of the proportions of the human body, distinguishing it from monkeys. Thus, humans are characterized by shorter upper limbs.

Upright walking and work led to the formation of asymmetry in the human body. Right and left half The human body is not symmetrical in shape and structure. A striking example this is the hand of man. Most people are right-handed, and about 2–5% are left-handed.

The development of upright walking, which accompanied the transition of our ancestors to living in open areas, led to significant changes in the skeleton and the entire body as a whole.

Question 1.
Skeleton performs the following functions:
1) supporting - for all other systems and organs;
2) motor - ensures the movement of the body and its parts in space;
3) protective - protects against external influences organs of the chest and abdominal cavity, brain, nerves, blood vessels.

Question 2.
Distinguish two types of skeleton– external and internal. Some protozoa, many mollusks, arthropods have an exoskeleton - these are the shells of snails, mussels, oysters, the hard shells of crayfish, crabs, and the light but durable chitinous coverings of insects. Invertebrate radiolarians, cephalopods and vertebrates have an internal skeleton.

Question 3.
The body of mollusks is usually enclosed in a shell. The sink may consist of two doors or be of another shape in the form of a cap, curl, spiral, etc. The shell is formed by two layers - the outer, organic, and the inner, made of calcium carbonate. The calcareous layer is divided into two layers: behind the organic layer lies a porcelain-like layer formed by prismatic crystals of calcium carbonate, and below it is a mother-of-pearl layer, the crystals of which have the shape of thin plates on which light interference occurs.
The shell is an external hard skeleton.

Question 4.
The body and limbs of insects have a chitinized cover - the cuticle, which is the exoskeleton. The cuticle of many insects is equipped big amount hairs that perform the function of touch.

Question 5.
Protozoa can form external skeletons in the form of shells or shells (foraminifera, radiolarians, armored flagellates), as well as internal skeletons of various shapes. The main function of the protozoan skeleton is protective.

Question 6.
The presence of hard covers in arthropods prevents the continuous growth of animals. Therefore, the growth and development of arthropods is accompanied by periodic molting. The old cuticle is shed, and until the new one hardens, the animal grows.

Question 7.
Vertebrates have an internal skeleton, the main axial element of which is the notochord. In vertebrates, the internal skeleton consists of three sections - the skeleton of the head, the skeleton of the trunk and the skeleton of the limbs. Vertebrates (amphibian fish, reptiles, birds, mammals) have an internal skeleton.

Question 8.
Plants then They also have supporting structures, with the help of which they carry the leaves towards the sun and maintain them in such a position that the leaf blades are illuminated as best as possible by sunlight. In woody plants, the main support is mechanical tissue. There are three types of mechanical fabrics:
1) collenchyma is formed from living cells of various shapes. They are found in young plant stems and leaves;
2) the fibers are represented by dead elongated cells with uniformly thickened membranes. Fibers are part of wood and bast. An example of non-lignified bast fibers is flax;
3) stony cells have irregular shape and highly thickened lignified shells. These cells form nut shells, stones of drupes, etc. Stony cells are found in the pulp of pear and quince fruits.
In combination with other tissues, mechanical tissue forms a kind of “skeleton” of the plant, especially developed in the stem. Here it often forms a kind of cylinder running inside the stem, or is located along it in separate strands, providing bending strength to the stem. In the root, on the contrary, the mechanical tissue is concentrated in the center, increasing the root's tensile strength. Wood also plays a mechanical role; even after dying, wood cells continue to perform a supporting function.

Lesson 24. MAMMAL SKELETON

Equipment and materials

1. Skeleton of a rabbit, cat or rat (one for two students).
2. Vertebrae from different parts of the body (one for two students).
3. Front and hind limbs with belts (one for two students).
4. Skulls of insectivores, rodents, carnivores, ungulates (one for two students).
5. Tables: 1) skeleton of a mammal; 2) the structure of vertebrae from different parts of the body; 3) skull (side and bottom view); 4) the skeleton of the limbs and their girdles.

Introductory Notes

The mammalian skeleton retains features typical of the amniote skeleton. It consists of the brain and visceral skulls, spine, chest, skeleton of the limbs and their girdles. The spine has a well-defined division into five sections: cervical, thoracic, lumbar, sacral and caudal. In the cervical region, with rare exceptions, there are always seven vertebrae. The first two vertebrae - the atlas and epistropheus - have the same structure as those of reptiles and birds. Mammalian vertebrae of the platycolic type have flat articular surfaces with cartilaginous discs.

The skull is characterized by an enlargement of the braincase, rather late fusion of a number of bones in ontogenesis with the formation of complex complexes, connection of bones with sutures, strong development ridges for muscle attachment. Due to the significant development of the olfactory organ, ethmoid bone. There are two occipital condyles. The visceral skeleton undergoes further changes: three bones appear in the cavity of the middle ear: the stirrup, the incus, and the malleus. In mammals - the tympanic bone. The lower jaw is represented by only one bone - the tooth. The jaws contain teeth. Like amphibians, but not like reptiles and birds, there are wrist and ankle joints.

Scull

Brain skull

Occipital region: occipital bone; foramen magnum; occipital condyles.

Sides of the skull: squamosal bones with zygomatic processes; zygomatic; maxillary; intermaxillary (premaxillary); lacrimal; oculocuneiform; pterygosphenoid bones.

Skull roof: parietal; interparietal; frontal; nasal bones.

Bottom of the skull: main wedge-shaped; anterior wedge-shaped; rocky; pterygoid; palatines; palatine processes of the maxillary bones; lattice labyrinths; vomer; tympanic bone; choanae; openings for the exit of nerves, blood vessels and the Eustachian tube.

Visceral skull

Lower jaw: dentaries with coronoid, articular and angular processes.

Spine

Spinal sections: cervical; chest; lumbar; sacral and caudal.

The structure of the trunk platycelium vertebra, atlas and epistropheus.

Rib cage: true and false edges; sternum (manubrium and xiphoid process).

Limb belts

Shoulder girdle: scapula, clavicle (no coracoids). Pelvic girdle: innominate bones (fused iliac, ischial and pubic bones).

Paired limbs

Forelimb: shoulder; forearm (radial and ulna); hand (wrist, metacarpus, phalanges).

Hind limb: hip; shin (tibia and fibula); foot (tarsus, metatarsus, phalanges).

Sketch:

skull (side and bottom view).

Skeletal structure

The skull of mammals is relatively large, which is due to the increase in the size of the braincase (Fig. 119). The bones are heavy and thick, connected to each other by sutures. The eye sockets are relatively small. Groups of bones grow together into complexes, which include, in particular, the occipital and petrous bones.

In mammals, two new bones appear - the ethmoid (in the nasal cavity) and the interparietal (roof of the skull). A number of ancestral bones undergo both structural and functional changes, especially in the visceral skeleton. In the region of the middle ear there are three auditory ossicles: the stapes (former hyomandibular bone, which first appeared in amphibians), the incus (former quadrate bone), and the malleus (former articular bone). The middle ear itself is covered by the tympanic bone (paired), characteristic only of mammals, derived from the angular bone. Thus, the lower jaw of mammals is formed only by a pair of integumentary dentary bones connected directly to the brain skull.

Mammals have a well-developed secondary hard palate and a unique zygomatic arch.

Rice. 119. Cat skull side view ( A), bottom ( B) and her lower jaw ( IN):
1 - occipital bone; 2 - occipital condyle, 3 - foramen magnum; 4 - parietal bone; 5 - interparietal bone; 6 - frontal bone; 7 - nasal bone; 8 - scaly bone; 9 - zygomatic process of the squamosal bone; 10 - cheekbone; 11 - auditory drum; 12 - auditory opening; 13 - pterygosphenoid bone; 14 - oculosphenoid bone; 15 - main sphenoid bone, 16 - anterior sphenoid bone; 17 - lacrimal bone; 18 - maxillary bone, 19 - premaxillary bone; 20 - palatine bone, 21 - pterygoid bone; 22 - dentary bone; 23 - coronoid process of the dentary; 24 - articular process of the dentary; 25 - angular process; 26 - petrous bone

Brain skull

Occipital region of the skull represented by one occipital bone surrounding the foramen magnum. On its sides there are two condyles that provide connection with the spine. The occipital bone is formed by the early fusion of four bones: the superior occipital, the two lateral occipitals and the basioccipital.

Sides of the skull in the posterior part they are limited by squamosal bones with highly developed zygomatic processes. The zygomatic process is directed forward and bears the articular surface for the lower jaw. It connects to the zygomatic bone, which in turn is attached to the zygomatic process of the maxillary bone. As a result, a zygomatic arch is formed, characteristic only of mammals. Adjacent to the squamosal bone is the petrous bone (fused ear bones of the ancestors).

Eye socket lined by the pterygosphenoid, oculosphenoid and lacrimal bones. The oculosphenoid bone forms the interorbital septum. In the posterior corner of the orbit lies the pterygosphenoid

bone, and in the anterior one - the lacrimal bone, penetrated by the lacrimal canal.

The ethmoid bone appears in the nasal cavity of mammals. Its middle part forms nasal septum. The appearance of this bone is associated with the superior development of the sense of smell in mammals.

Skull roof formed by paired bones of cutaneous origin: nasal, frontal and parietal. The latter in some mammals fuse into one bone. Between the parietal and occipital bones there is an interparietal bone, characteristic only of mammals. It can remain independent or fuse with neighboring bones.

Behind bottom of the skull formed partly by the occipital bone. In front of it is the main sphenoid bone. In all amniotes this bone is well developed. In front of it is the anterior sphenoid bone, protruding forward as a small wedge. In the back of the bottom of the skull, paired swellings are clearly visible - the tympanic bones, covering the cavity of the middle ear. These bones are derived from the angular bone (visceral skeleton) of the ancestors. They open outward through the ear canal. The anterior part of the bottom of the skull is represented by a secondary structure characteristic of mammals. hard palate, formed by the palatine bones and palatine processes of the premaxillary and maxillary bones. This device allows the animal to breathe while chewing food.

Visceral skull

Visceral, or facial, skull mammals has characteristic features. The secondary upper jaw, as in all higher vertebrates, is tightly fused with the brain skull. The lower jaw is represented by only one bone - the tooth. This feature is a good marking of the difference between the skull of mammals and the skull of other vertebrates. Dental bone has three processes: coronoid, articular and angular. This bone bears teeth. The articular process with its convex surface connects with the zygomatic process of the squamosal bone, on which there is an articular surface. Thus, there is a direct articulation of the lower jaw with the brain skull, bypassing the inserted elements of the visceral skeleton of all other vertebrates.

Maxillary and premaxillary bones ( secondary maxilla) in mammals, as in all amniotes, grow to brain skull, forming its anterior section. These bones bear teeth.

During embryonic development in mammals, as well as in other vertebrates, the palatoquadrate and Meckel's cartilages develop ( primary jaw arch). The posterior part of the palatoquadrate cartilage ossifies into a quadrate bone, which in all vertebrates, starting with teleost fish, serves as the attachment site for the lower jaw. In mammals, the quadrate bone is transformed into the auditory ossicle - the incus. Meckel's cartilage also ossifies. In bony fishes it is replaced by the articular and angular bones. In mammals, the articular bone turns into another auditory bone - the malleus. The angular bone, as already mentioned, forms the tympanic bone.

Upper section hyoid arch- the hyomandibular, starting with amphibians, is transformed into an auditory ossicle - the stapes. Lower section The hyoid arch (hyoid and copula), as well as the first branchial arch in mammals, are represented by the hyoid bone with anterior and posterior horns. The remaining elements of the gill arches are transformed into laryngeal cartilage.

Spine

The spinal column of mammals is represented by five sections: cervical, thoracic, lumbar, sacral and caudal (Fig. 120). Vertebrae platycoelous type, the surface of the vertebral body is flat. Between them are cartilaginous layers, or menisci.

For cervical region Characteristically, there is a constant number of vertebrae - seven. Thus, the length of the neck of mammals depends on the size of the vertebrae themselves, and not on their number. Thus, giraffes, whales and moles have the same number of cervical vertebrae. Only the manatee (siren order) and sloths (edentate order) have a different number of cervical vertebrae (6 - 10).

The first two cervical vertebrae in mammals, like all amniotes, are transformed. The ring-shaped atlas rotates around its own body- odontoid process attached to the body of the second vertebra - epistrophy (Fig. 121). The atlas bears two articular surfaces for connection with the condyles of the skull.

The remaining vertebrae are of a typical structure (Fig. 122). Each vertebra consists of a body, a superior arch with a superior spinous process, and transverse processes. The vertebrae have cartilaginous articular surfaces for movable connection with each other.

IN thoracic region the number of vertebrae varies from 9 to 24, although usually it is 12 - 13. The spinous processes of the vertebrae are large,

Rice. 120. Rabbit skeleton:
1 - cervical vertebrae; 2 - thoracic vertebrae; 3 - lumbar vertebrae; 4 - sacrum; 5 - caudal vertebrae; 6 - ribs; 7 - manubrium of the sternum; 8 - shoulder blade; 9 - acromial process of the scapula; 10 - coracoid process of the scapula; 11 - ilium of the innominate bone; 12 - ischial region innominate bone; 13 - pubic section of the innominate bone; 14 - obturator foramen; 15 - brachial bone; 16 - elbow bone; 17 - radius bone; 18 - wrist; 19 - metacarpus; 20 - hip; 21 - knee cap; 22 - tibia; 23 - fibula; 24 - calcaneus; 25 - the remaining bones of the tarsus; 26 - metatarsus; 27 - olecranon

directed backwards. The ribs are attached to the thick and short transverse processes.

Vertebrae lumbar region massive, do not have ribs (they are rudimentary). Their number varies in different species from 2 to 9. Their spinous processes are small, directed forward towards those of the thoracic vertebrae.

Rice. 121. The first two cervical vertebrae of a mammal:
A- atlas; B- epistrophe (from above and from the side); 1 - transverse process; 2 - odontoid process; 3 - superior spinous process
Rice. 122. Side view of the thoracic vertebra of a cat ( A) and front ( B):
1 - vertebral body; 2 - upper arc; 3 - superior spinous process; 4 - transverse processes

Sacral the vertebrae fuse together to form the sacrum. A powerful sacrum helps to strengthen the connection through the girdle of the hind limbs with the axial skeleton. The number of sacral vertebrae is usually 2 - 4, although it can reach 10 (in edentates). Moreover, there are usually 2 true sacral ones, the rest are initially caudal ones.

Tails the vertebrae have shortened processes. The number of caudal vertebrae varies from 3 (gibbon) to 49 (long-tailed lizard). It is interesting to note that some apes have fewer caudal vertebrae than humans. For example, an orangutan has 3 of them, a human has 3 - 6 (usually 4).

Rib cage

The thorax of mammals is formed by the sternum and ribs, attached at one end to the sternum and at the other to the transverse processes of the thoracic vertebrae. Sternum- a segmented plate consisting of an upper part - the manubrium - and a lower part - the xiphoid process. Ribs They are divided into true ones, which articulate with the sternum (in mammals there are usually seven of them), and false ones, which do not reach the sternum.

Limb belts

Shoulder girdle All tetrapods are normally formed by paired bones: the scapula, coracoid and clavicle. In mammals, not all elements of the shoulder girdle of terrestrial vertebrates are developed (Fig. 123).

The scapula is a wide triangular bone lying on top of the rib cage. A ridge ending in the acromion process is clearly visible on it. The ridge serves to attach muscles.

The coracoid is present only in oviparous mammals. The rest

Rice. 123. Shoulder girdle and forelimb of a fox:
1 - shoulder blade; 2 - ridge of the scapula; 3 - acromion process; 4 - articular fossa; 5 - coracoid process; 6 - brachial bone; 7 - elbow bone; 8 - radius bone; 9 - wrist; 10 - metacarpus; 11 - phalanges of fingers

(of real animals) the coracoid in the form of a separate bone exists only in the embryonic state. During ontogenesis, it grows to the scapula, forming a coracoid process. This process is directed forward and hangs somewhat over humerus.

The collarbone is a rod-shaped bone that connects the scapula to the sternum. The clavicle not only strengthens the articular fossa, attaching the shoulder girdle to the chest, but also allows the forelimb to make movements in different planes in many animals (for example, moles, monkeys, bats, bears). In fast running and jumping mammals, whose forelimbs move in one plane (forward and backward), the clavicle is reduced. Thus, it is absent in ungulates, some carnivores, and proboscis. In these animals, the shoulder girdle (more precisely, the scapula) is connected to the axial skeleton only by ligaments and muscles.

Pelvic girdle mammals (Fig. 124) is typical of tetrapods. It is represented by paired innominate bones, which were formed as a result of the fusion of three pairs of bones: the ilium, the ischium and the pubis. The ilium of the innominate bone, as usual, is directed upward and connected to the sacral vertebrae (sacrum); sciatic - go down and back; pubic - down and forward. Below, the innominate bones fuse to form the symphysis. Thus, the pelvis in mammals, like in reptiles, is closed. At the bottom of the innominate bone there is an obturator foramen. At the point of connection of all three sections of the pelvic girdle, the acetabulum is formed - the place of articulation of the hind limb. In cloacals and marsupials, dermal marsupial bones are adjacent to the pubic region.

Paired limbs

The skeleton of the paired limbs of mammals has all the typical features of the original five-fingered limb of tetrapods. It is a complex lever consisting of three sections. In the forelimb these are the shoulder, forearm and hand; in the back - thigh, lower leg and foot. The joints between the lower leg and foot (ankle), as well as the forearm and hand (anterocarpal) are of the “amphibian” type, in contrast to reptiles and birds, in which these joints are formed respectively between the bones of the metatarsus and the bones of the wrist.

In the forelimb, the shoulder is formed by the humerus (see Fig. 123). The forearm consists of the radius and ulna bones. The radius goes in the direction of the first (inner) finger. The ulna is directed towards the last (outer) finger. In the upper part it has an olecranon process. The hand, in turn, is formed by three sections: the wrist, metacarpus and phalanges of the fingers. The wrist consists of 8 - 10 bones arranged in 3 rows. There are five bones in the metacarpus and the same number of fingers. The fingers usually have three phalanges, with the exception of the first, which has two phalanges.

The hind limb of mammals (see Fig. 124) consists of three sections: thigh, lower leg and foot. The thigh is represented by a massive elongated femur. The lower leg is formed by two bones - the tibia and fibula. They are the same in length, but differ in thickness and position. The large tibia occupies an internal position and is directed towards the first finger. The fibula is located on the outside and approaches the last (outer) finger. The joint between the thigh and lower leg is covered in front, characteristic of mammals. kneecap, formed from ossified muscle tendons. The foot is represented by three rows of tarsal bones. Among them, the heel bone stands out especially. There are five bones in the metatarsus. Fingers are attached to them. The fingers usually have three phalanges, with the exception of the thumb (inner) finger, which most often has two phalanges.

Due to the existence of mammals in a variety of conditions and their adaptation to various types movements of the described type of limbs undergoes changes in some representatives. In all animals, the nature of whose movement is associated with fast running or jumping, one bone remains in the lower leg, and often in the forearm, respectively, the tibia and ulna (ungulates, canines, kangaroos, jerboas, etc.). In addition, they are characterized by the appearance of additional

lever and shock absorber: the metatarsal bones lengthen and merge into one. Good runners reduce the number of toes from five to four (even-toed ungulates) and even to one (odd-toed ungulates). In artiodactyls, digits III and IV receive primary development, in equids - III. In bats, the phalanges I - V of the toes of the front paws are elongated, and a leathery wing membrane is stretched between them. Among mammals there are plantigrade walkers (bears, hedgehogs, moles, monkeys) and digitigrade walkers (ungulates, canines).

During veterinary-sanitary or forensic examinations, the doctor has to determine the type of animal from the carcass, corpse, their parts or individual bones. Often the decisive factor is the presence or absence of some detail or shape feature. Knowledge of comparative anatomical features The structure of the bones allows us to confidently draw a conclusion about the type of animal.

CERVICAL VERTEBRA - vertebrae cervicales.

Atlas - atlas - first cervical vertebra (Fig. 22).

At the large cattle The transverse processes (wings of the atlas) are flat, massive, set horizontally, their caudolateral acute angle is pulled back, the dorsal arch is wide. The wing has an intervertebral and alar foramen, but no transverse one.

The ovine caudal margin of the dorsal arch has a deeper, gentle notch, and there are also only two openings on the wing.

Rice. 22. Atlas cows (I), sheep Ш), goats (III), horses (IV), pigs (V), dogs (VI)

In goats, the lateral edges of the wings are slightly rounded, and the caudal notch of the dorsal arch is deeper and narrower than in sheep and cattle, and there is no transverse foramen.

In horses, on significantly developed, thinner, inclined wings, in addition to the alar and intervertebral foramina, there is a transverse foramen. The caudal edge of the dorsal arch has a deep, gently sloping notch.

In pigs, all cervical vertebrae are very short. Atlas has massive narrow wings with thickened rounded edges. The wing has all three openings, but the transverse one can be seen only along the caudal edge of the atlas wings, where it forms a small canal.

In dogs, the atlas has widely spaced lamellar wings with a deep triangular notch along its caudal margin. There are both intervertebral and transverse foramina, but instead of the alar foramen there is an alar notch - incisure alaris.

Axis, or epistropheus, - axis s. epistropheus - second cervical vertebra (Fig. 23).

Rice. 23. Axis (epistrophe) of a cow (1), sheep (II), goat (III), horse (IV), pig (V), dog (VI)

Rice. 24. Cervical vertebrae (middle) cow* (O, horses (II), pigs (III), dogs (IV)

In cattle, the axial vertebra (epistropheus) is massive. The odontoid process is lamellar, semi-cylindrical in shape. The crest of the axial vertebra is thickened along the dorsal edge, and the caudal articular processes at its base project independently.

In horses, the axial vertebra is long, the odontoid process is wide, flattened, the crest of the axial vertebra bifurcates in the caudal part, and on the ventral side of this bifurcation lie the articular surfaces of the caudal articular processes.

In pigs, the epistrophy is short, the odontoid process in the form of a wedge has a conical shape, the ridge is high (increases in the caudal part).

In dogs, the axial vertebra is long, with a long wedge-shaped odontoid process; the crest is large, lamellar, protrudes forward and hangs over the odontoid process.

Typical cervical vertebrae - vertebrae cervicales - third, fourth and fifth (Fig. 24).

In cattle, the typical cervical vertebrae are shorter than in the horse, the fossa and head are well defined. In the bifurcated transverse process, its cranioventral part (costal process) is large, lamellar, extended downward, the caudodorsal branch is directed laterally. The spinous processes are round, well defined and directed cephalad.

Horses have long vertebrae with a well-defined head, fossa and ventral ridge. The transverse process is bifurcated along the sagittal plane, both parts of the process are approximately equal in size. There are no spinous processes (in their place there are scallops).

Pig vertebrae are short, the head and fossa are flat. The costal processes are wide below, oval-rounded, drawn down, and the caudodorsal plate is directed laterally. There are spinous processes. An additional cranial intervertebral foramen is very typical for the cervical vertebrae of pigs.

Dogs have typical cervical vertebrae that are longer than pigs, but the head and fossa are also flat. The plates of the transverse costal process are almost identical and bifurcate along the same sagittal plane (as in the horse). Instead of spinous processes there are low ridges.

Sixth and seventh cervical vertebrae.

In cattle, on the sixth cervical vertebra, the powerful plate of the costal process extended ventrally has a square shape; on the body of the seventh there is a pair of caudal costal facets; the transverse process is not bifurcated. The lamellar spinous process is high. There is no transverse hole, like the horse and pig.

In horses, the sixth vertebra has three small plates on the transverse process, the seventh is massive, does not have a transverse foramen, is shaped like the first thoracic vertebra of a horse, but has only one pair of caudal costal facets and a low spinous process on the body.

Rice. 25. Thoracic vertebrae of a cow (I), horse (II), pig (III), dog (IV)

The sixth vertebra of the pig has a wide powerful plate of the transverse process extended ventrally oval shape, on the seventh, the intervertebral foramina are double and the spinous process is high, lamellar, set vertically.

In dogs, the sixth vertebra has a wide plate of the costal process beveled from front to back and downwards; on the seventh, the spinous process is set perpendicularly, has an awl-shaped shape, caudal costal facets may be absent.

Thoracic vertebrae - vertebrae thoracicae (Fig. 25).

Cattle have 13 vertebrae. In the area of ​​the withers, the spinous processes are wide, lamellar, and caudally inclined. Instead of a caudal vertebral notch, there may be an intervertebral foramen. The diaphragmatic vertebra is the 13th with a vertical spinous process.

Horses have 18-19 vertebrae. In the area of ​​the withers, the 3rd, 4th and 5th spinous processes have club-shaped thickenings. The articular processes (except the 1st) have the appearance of small contiguous articular surfaces. Diaphragmatic vertebra - 15th (sometimes 14th or 16th).

Pigs have 14-15 vertebrae, maybe 16. The spinous processes are wide, lamellar, vertically set. At the base of the transverse processes there are lateral openings running from top to bottom (dorsoventrally). There are no ventral ridges. Diaphragmatic vertebra - 11th.

Dogs have 13 vertebrae, rarely 12. The spinous processes in the withers area at the base are curved and directed caudally. The first spinous process is the highest; on the latter, accessory and mastoid processes run ventrally from the caudal articular processes. Diaphragmatic vertebra - 11th.

Lumbar vertebrae - vertebrae lumbales (Fig. 26).

Cattle have 6 vertebrae. They have a long body, slightly narrowed in the middle part. ventral ridge. The transverse costal (transverse) processes are dorsally (horizontally) located, long, lamellar, with pointed, uneven edges and ends curved cranially. The articular processes are powerful, widely spaced, with strongly concave or convex articular surfaces.

Horses have 6 vertebrae. Their bodies are shorter than those of cattle, the transverse costal processes are thickened, especially the last two or three, on which flat articular surfaces are located along the cranial and caudal edges (in old horses they often synostose). The caudal surface of the transverse costal process of the sixth vertebra is connected by a joint to the cranial edge of the wing of the sacral bone. Normally, there is never synostosis here. The articular processes are triangular in shape, less powerful, closer together, with flatter articular surfaces.

Rice. 26. Lumbar vertebrae of a cow (I), horse (I), pig (III), dog (IV)

Pigs have 7, sometimes 6-8 vertebrae. The bodies are long. The transverse costal processes are horizontally located, lamellar, slightly curved, have lateral notches at the base of the caudal edge and lateral openings closer to the sacrum. The articular processes, like those of ruminants, are powerful, widely spaced, strongly concave or convex, but, unlike ruminants, they have mastoid processes, making them more massive.

Dogs have 7 vertebrae. The transverse costal processes are lamellar and directed cranioventrally. The articular processes have flat articular, slightly inclined surfaces. The accessory and mastoid (on the cranial) processes are strongly pronounced on the articular processes.

The sacral bone is os sacrum (Fig. 27).

In cattle, 5 vertebrae are fused. They have massive quadrangular wings located almost on a horizontal plane, with a slightly raised cranial edge. The spinous processes have fused to form a powerful dorsal ridge with a thickened edge. The ventral (or pelvic) sacral foramina are extensive. Complete synostosis of the vertebral bodies and arches normally occurs by 3-3.5 years.

In horses, 5 fused vertebrae have horizontally located triangular-shaped wings with two articular surfaces - auricular, dorsal for connection with the wing of the iliac bone of the pelvis and cranial for connection with the transverse costal process of the sixth lumbar vertebra. The spinous processes grow together only at the base.

In pigs, 4 vertebrae are fused. The wings are rounded, placed along the sagittal plane, the articular (ear-shaped) surface is on their lateral side. There are no spinous processes. Interarch openings are visible between the arches. Normally, synostosis occurs by 1.5-2 years.

In dogs, 3 vertebrae are fused. The wings are rounded, set, like those of a pig, in the sagittal plane with a laterally located articular surface. In the 2nd and 3rd vertebrae the spinous processes are fused. Synostosis is normal by 6-8 months.

Tail vertebrae - vertebrae caudales s. coccygeae (Fig. 28),

Cattle have 18-20 vertebrae. Long, on the dorsal side of the first vertebrae rudiments of arches are visible, and on the ventral side (on the first 9-10) there are paired hemal processes, which can form hemal arches on the 3rd-5th vertebrae. "The transverse processes are wide, lamellar, curved ventrally.

Fig 27. Sacral bone of a cow (1), sheep (I), goat (III), horse (IV), pig (V), dog (VI)

Horses have 18-20 vertebrae. They are short, massive, retain arches without spinous processes; only on the first three vertebrae the transverse processes are flat and wide, disappearing on the last vertebrae.

Pigs have 20-23 vertebrae. They are long, arched with spinous processes, inclined caudally, preserved on the first five to six vertebrae, which are flatter, then become cylindrical. The transverse processes are wide.

Rice. 28. Caudal vertebrae of a cow (I), horse (II), pig (III), dog (IV)

Dogs have 20-23 vertebrae. On the first five to six vertebrae, the arches, cranial and caudal articular processes are preserved. The transverse processes are large, long, extended caudoventrally.

Ribs - costae (Fig. 29, 30).

Cattle have 13 pairs of ribs. They have a long neck. The first ribs are the strongest and the shortest and straightest. The middle ones are lamellar, widening significantly downwards. They have a thinner caudal edge. The hind ones are more convex, curved, with the head and tubercle of the ribs closer together. The last rib is short, thins downward, and may be hanging. It can be felt in the upper third of the costal arch.

Synostosis of the head and tubercle of the rib with the body in young animals does not occur simultaneously and goes from front to back. The first to fuse with the body is the head and tubercle of the first rib. The articular surface of the tubercle is saddle-shaped. The sternal ends of the ribs (2nd to 10th) have articular surfaces for connection with the costal cartilages, which have articular surfaces at both ends. There are 8 pairs of sternal ribs.

Horses have 18-19 pairs of ribs. Most of them are of uniform size along the entire length, the first is significantly expanded ventrally, up to the tenth the curvature and length of the ribs increase, then begin to decrease. The first 6-7 ribs are the widest and most lamellar. Unlike ruminants, their caudal edges are thicker and their neck is shorter. The tenth rib is almost tetrahedral. There are 8 pairs of sternal ribs.

Pigs often have 14, maybe 12 or up to 17 pairs of ribs. They are narrow, from the first to the third or fourth the width increases slightly. They have articular surfaces for connection with the costal cartilages. In adults, the sternal ends are narrowed, in piglets they are slightly widened. On the tubercles of the ribs there are small flat statutory facets; the bodies of the ribs have a faintly visible spiral turn. There are 7 (6 or 8) pairs of sternal ribs.

Dogs have 13 pairs of ribs. They are arched, especially in the middle part. Their length increases to the seventh rib, their width to the third or fourth, and their curvature to the eighth rib. On the tubercles the facet ribs are convex, there are 9 pairs of sternal ribs.

The breast bone is sternum (Fig. 31).

In cattle it is powerful and flat. The handle is rounded, raised, does not protrude beyond the first ribs, and is connected to the body by a joint. The body expands caudally. On the xiphoid process there is a significant plate of xiphoid cartilage. Along the edges there are 7 pairs of articular costal fossae.

In horses it is laterally compressed. It has a significant cartilaginous addition on the ventral edge, forming a ventral ridge, which protrudes on the handle, rounding, and is called a hawk. In adult animals, the manubrium and body are fused. Cartilage without xiphoid process. Along the dorsal edge of the sternum there are 8 pairs of articular costal fossae.

Rice. 29. Ribs of a cow (I), horse (II)

Rice. 30. Vertebral end of horse ribs

Rice. 31. Cow breast bone (I). sheep (II), goats (III), horses (IV), pigs (V), dogs (VI)

In pigs, like in cattle, it is flat, connected to the handle by a joint. The handle, unlike ruminants, in the form of a rounded wedge protrudes in front of the first pairs of ribs. The xiphoid cartilage is elongated. On the sides there are (7-8) pairs of articular costal fossae.

In dogs, it is in the form of a round, bead-shaped stick. The handle protrudes in front of the first ribs with a small tubercle. The xiphoid cartilage is rounded, on the sides there are 9 pairs of articular costal fossae.

Chest - thorax.

In cattle it is very voluminous, in the front part it is laterally compressed, and has a triangular exit. Behind the shoulder blades it expands strongly in the caudal direction.

In horses, it is cone-shaped, long, slightly compressed from the sides, especially in the area where the shoulder girdles are attached.

In pigs, it is long, laterally compressed, the height and width vary among different breeds.

Dogs are cone-shaped with steep sides, the inlet is rounded, the intercostal spaces - spatia intercostalia - are large and wide.

Self-test questions

1. What is the importance of the movement apparatus in the life of the body?

2. What functions does the skeleton perform in the body in mammals and birds?

3. What stages of development in phylo- and ontogenesis do the internal and external skeletons of vertebrates go through?

4. What changes occur in the bones with increasing static load (with limited motor activity)?

5. How is bone built as an organ and what differences are there in its structure in young growing organisms?

6. What sections is the vertebral column divided into in terrestrial vertebrates and how many vertebrae are there in each section in mammals?

7. In which part of the axial skeleton is there a complete bone segment?

8. What are the main parts of a vertebra and what parts are located on each part?

9. In which parts of the spinal column did the vertebrae undergo reduction?

10. By what features will you distinguish the vertebrae of each section of the spinal column and by what features will you determine the species characteristics of the vertebrae of each section?

11. What characteristic features structures have an atlas and an axial vertebra (epistropheus) in domestic animals? What is the difference between the atlas of pigs and the axial vertebra of ruminants?

12. By what feature can you distinguish the thoracic vertebra from the other vertebrae of the spinal column?

13. By what features can you distinguish the sacral bone of cattle, horses, pigs and dogs?

14. Name the main features of the structure of a typical cervical vertebra in ruminants, pigs/horses and dogs.

15. Which one is the best? characteristic feature have lumbar vertebrae? How do they differ between ruminants, pigs, horses and dogs?

Vertebrate skeleton formed not only by bones: it includes cartilage and connective tissue, and sometimes it includes various skin formations.

In vertebrates it is customary to distinguish axial skeleton(skull, chord, spine, ribs) and limb skeleton, including their belts (shoulder and pelvic) and free departments. Snakes, legless lizards and caecilians lack the skeleton of limbs, although some species of the first two groups retain their rudiments. In eels, the pelvic fins corresponding to the hind limbs have disappeared. Whales and sirens have no external signs the hind legs were also gone.

Scull. Based on their origin, there are three categories of skull bones:

• replacing cartilage,
• integumentary (overlay, or skin)
• visceral.

In sharks and their relatives, it may once have contained bones, but now its box is a single monolith of cartilage with no seams between the elements. Bony fish have more in their skull various bones than in representatives of any other class of vertebrates. In them, like all higher groups, the central bones of the head are embedded in cartilage and replace it, and therefore are homologous to the cartilaginous skull of sharks.

Visceral elements of the skull- derivatives of cartilaginous gill arches that arose in the walls of the pharynx during the development of gills in vertebrates. In fish, the first two arches have changed and turned into maxillary and sublingual apparatus. In typical cases, they retain 5 more gill arches, but in some genera their number has decreased. The primitive modern sevengill shark (Heptanchus) has as many as seven gill arches behind the jaw and hyoid arches. In bony fishes, the jaw cartilages are lined with numerous integumentary bones; the latter also form gill covers that protect the delicate gill filaments. During the evolution of vertebrates, the original jaw cartilages were steadily reduced until they disappeared completely. If in crocodiles the remainder of the original cartilage in the lower jaw is lined with 5 paired integumentary bones, then in mammals only one of them remains - the tooth, which completely forms the skeleton of the lower jaw.

The skull of ancient amphibians contained heavy integumentary plates and was similar in this respect to the typical skull of lobe-finned fish. In modern amphibians, both applique and replacement bones are greatly reduced. There are fewer of them in the skull of frogs and salamanders than in other vertebrates with a bony skeleton, and in the latter group many elements remain cartilaginous. In turtles and crocodiles, the skull bones are numerous and tightly fused to each other. In lizards and snakes they are relatively small, with the external elements separated by wide intervals, as in frogs or toads. In birds, the skull bones are thin but very hard; in adults they have fused so completely that several sutures have disappeared. The orbital sockets are very large; the roof of the relatively huge braincase is formed by thin integumentary bones; the light jaws are covered with horny sheaths. In mammals, the skull is heavy and includes powerful jaws with teeth. The remains of the cartilaginous jaws moved to the middle ear and formed its bones - the hammer and the incus.

In birds and reptiles, the skull is attached to the spine using one of its condyle(articular tubercle). In modern amphibians and all mammals, two condyles located on the sides of the spinal cord are used for this.

Spine, in embryonic development it is always preceded by chord, which persists for life in lancelets and cyclostomes. In fish, it is surrounded by vertebrae (in sharks and their closest relatives - cartilaginous) and looks clear-shaped. In mammals, only rudiments of the notochord are preserved intervertebral discs. The notochord is not transformed into vertebrae, but is replaced by them. They arise during embryonic development as curved plates that gradually surround the notochord in rings and, as they grow, almost completely displace it.

A typical spine has 5 sections:

• cervical,
• thoracic (corresponding to the chest),
• lumbar,
• sacral
• tail.

Number cervical vertebrae varies greatly depending on the group of animals. Modern amphibians have only one such vertebra. Small birds can have as few as 5 vertebrae, while swans can have up to 25. The Mesozoic marine reptile plesiosaur had 72 cervical vertebrae. In mammals there are almost always 7 of them; the exception is sloths (from 6 to 9). The first cervical vertebra is called atlas. In mammals and amphibians it has two articular surfaces, which include the occipital condyles. In mammals the second cervical vertebra ( epistrophy) forms the axis on which the atlas and skull rotate.

TO infant Ribs are usually attached to the vertebrae. Birds have about five, mammals have 12 or 13; snakes have a lot. The bodies of these vertebrae are usually small, and the spinous processes of their upper arches are long and inclined backwards.Lumbar vertebrae usually from 5 to 8; in most reptiles and all birds and mammals they do not bear ribs. The spinous and transverse processes of the lumbar vertebrae are very powerful and, as a rule, directed forward. In snakes and many fish, the ribs are attached to all the trunk vertebrae, and it is difficult to draw the boundary between the thoracic and lumbar regions. In birds, the lumbar vertebrae are fused with the sacral vertebrae, forming a complex sacrum, which makes their back more rigid than that of other vertebrates, with the exception of turtles, in which the thoracic, lumbar and sacral regions are connected to the shell.

Number sacral vertebrae varies from one in amphibians to 13 in birds.Structure tail The department is also very diverse; in frogs, birds, apes and humans it contains only a few partially or completely fused vertebrae, and in some sharks it contains up to two hundred. Toward the end of the tail, the vertebrae lose their arches and are represented by only bodies.

Ribs first appear in sharks in the form of small cartilaginous processes in the connective tissue between muscle segments. In bony fishes they are bony and homologous to the haemal arches located below on the caudal vertebrae. In four-legged animals, such fish-type ribs, called lower, are replaced by upper ones and are used for breathing. They are laid in the same connective tissue partitions between muscle blocks as in fish, but are located higher in the body wall.

Skeleton limbs. The limbs of tetrapods developed from the paired fins of lobe-finned fish, the skeleton of which contained elements homologous to the bones of the shoulder and pelvic girdle, as well as the front and hind legs.Originally there were at least five separate ossifications in the shoulder girdle, but in modern animals there are usually only three: scapula, clavicle and coracoid. In almost all mammals, the coracoid is reduced, attached to the scapula, or absent altogether. In some animals, the scapula remains the only functional element of the shoulder girdle.

Pelvic girdle includes three bones:

• ileum,
• ischial
• pubic

In birds and mammals they completely merged with each other, in the latter case forming the so-called innominate bone. In fish, snakes, whales and sirens, the pelvic girdle is not attached to the spine, which therefore lacks the typical sacral vertebrae. In some animals, both the shoulder and pelvic girdles include accessory bones.

Bones anterior free limb and in quadrupeds they are basically the same as in the back, but are called differently. In the forelimb, if you count from the body, first comes humeral bone behind it radial And ulna bones, then carpals, metacarpals And phalanges of fingers.

IN hind limb they correspond femoral, then tibia and tibia, tarsal, metatarsals and phalanges. The initial number of fingers is 5 on each limb. Amphibians have only 4 toes on their front paws. In birds, the forelimbs are transformed into wings; the bones of the wrist, metacarpus and fingers are reduced in number and partially fused to each other, the fifth finger on the legs is lost. The horses only have their middle finger left. Cows and their closest relatives rest on the third and fourth toes, and the rest are lost or reduced. Ungulates move on their toes and are called phalanges. Cats and many other animals, when walking, rely on the entire surface of their fingers and belong to finger-walker type. When moving, bears and humans press their entire sole to the ground and are called plantigrade.

Exoskeleton. Vertebrates of all classes have an exoskeleton in one way or another. The head plates of scutes (extinct jawless animals), ancient fish and amphibians, as well as the scales, feathers and hair of higher tetrapods, are skin formations. The shell of turtles is of the same origin - a highly specialized skeletal formation. Their skin bone plates (osteoderms) moved closer to the vertebrae and ribs and merged with them. It is noteworthy that the shoulder and pelvic girdles parallel to this have shifted inside the chest. In the crest on the back of crocodiles and the shell of armadillos there are bone plates of the same origin as the shell of turtles