The musculoskeletal system ensures movement and preservation of the animal’s body position in space, forms the external shape of the body and participates in metabolic processes. It accounts for about 60% of the body weight of an adult animal.

Conventionally, the musculoskeletal system is divided into passive and active parts. TO passive part include bones and their connections, on which the nature of the mobility of bone levers and links of the animal’s body depends (15%). Active part consists of skeletal muscles and their auxiliary attachments, thanks to the contractions of which the bones of the skeleton are set in motion (45%). Both active and passive parts have a common origin (mesoderm) and are closely interconnected.

Functions of the motion apparatus:

1) Motor activity is a manifestation of the vital activity of the organism; it is what distinguishes animal organisms from plant organisms and determines the emergence of a wide variety of modes of movement (walking, running, climbing, swimming, flying).

2) The musculoskeletal system forms the shape of the body - exterior animal, since its formation occurred under the influence of the Earth’s gravitational field, its size and shape in vertebrate animals are distinguished by significant diversity, which is explained by different living conditions (terrestrial, terrestrial-woody, airy, aquatic).

3) In addition, the movement apparatus provides a number of vital functions of the body: searching and capturing food; attack and active defense; carries out respiratory function lungs (respiratory motor skills); Helps the heart move blood and lymph through the vessels (“peripheral heart”).

4) In warm-blooded animals (birds and mammals), the movement apparatus ensures the maintenance of a constant body temperature;

The functions of the movement apparatus are provided by the nervous and cardiovascular systems , respiratory, digestive and urinary organs, skin, glands internal secretion. Since the development of the movement apparatus is inextricably linked with the development of the nervous system, when these connections are disrupted, first paresis, and then paralysis movement apparatus (the animal cannot move). With a decrease in physical activity, metabolic processes are disrupted and muscle and bone tissue atrophy.

The organs of the musculoskeletal system have properties of elastic deformations, when moving, mechanical energy arises in them in the form of elastic deformations, without which normal blood circulation and impulses of the brain and spinal cord. The energy of elastic deformations in bones is converted into piezoelectric energy, and in muscles into thermal energy. The energy released during movement displaces blood from the vessels and causes irritation of the receptor apparatus, from which nerve impulses enter the central nervous system. Thus, the work of the movement apparatus is closely connected and cannot be carried out without the nervous system, and vascular system in turn, cannot function normally without a movement apparatus.

The basis of the passive part of the movement apparatus is the skeleton. Skeleton (Greek sceletos - dried, dried; lat. Skeleton) are bones connected in a certain order that form a solid frame (skeleton) of the animal’s body. Since the Greek word for bone is “os,” the science of the skeleton is called osteology.

The skeleton includes about 200-300 bones (Horse, r.s. -207-214; pig, dog, cat -271-288), which are connected to each other by connective, cartilaginous or bone tissue. The skeletal mass of an adult animal ranges from 6% (pig) to 15% (horse, cattle).

All skeletal functions can be divided into two large groups: mechanical and biological. TO mechanical functions include: protective, support, locomotor, spring, anti-gravity, and biological – metabolism and hematopoiesis (hemocytopoiesis).

1) Protective function is that the skeleton forms the walls of body cavities in which vital organs are located. For example, the cranial cavity contains the brain, the chest contains the heart and lungs, and the pelvic cavity contains the genitourinary organs.

2) The supporting function is that the skeleton provides support for muscles and internal organs, which are attached to the bones and are held in their position.

3) The locomotor function of the skeleton is manifested in the fact that the bones are levers that are driven by muscles and ensure the movement of the animal.

4) The spring function is due to the presence in the skeleton of formations that soften shocks and shocks (cartilaginous pads, etc.).

5) The anti-gravity function is manifested in the fact that the skeleton creates support for the stability of the body rising above the ground.

6) Participation in metabolism, especially mineral metabolism, since bones are a depot mineral salts phosphorus, calcium, magnesium, sodium, barium, iron, copper and other elements.

7) Buffer function. The skeleton acts as a buffer that stabilizes and maintains a constant ionic composition of the internal environment of the body (homeostasis).

8) Participation in hemocytopoiesis. Red located in the bone marrow cavities Bone marrow produces blood cells. The mass of bone marrow in relation to the mass of bones in adult animals is approximately 40-45%.

SKELETAL DIVISION

The skeleton is the frame of an animal's body. It is usually divided into main and peripheral.

To the axial skeleton include the skeleton of the head (skull-cranium), the skeleton of the neck, torso and tail. The most complex structure has a skull, since it contains the brain, organs of vision, smell, balance and hearing, oral and nasal cavities. The main part of the skeleton of the neck, body and tail is spinal column(columna vertebralis).

The spinal column is divided into 5 sections: cervical, thoracic, lumbar, sacral and caudal. The cervical region consists of the cervical vertebrae (v.cervicalis); thoracic region - from the thoracic vertebrae (v.thoracica), ribs (costa) and sternum (sternum); lumbar - from the lumbar vertebrae (v.lumbalis); sacrum - from the sacrum bone (os sacrum); caudal - from the caudal vertebrae (v.caudalis). The thoracic section of the body has the most complete structure, where there are thoracic vertebrae, ribs, and breast bone, which together form chest(thorax), in which the heart, lungs, and mediastinal organs are located. The tail region is the least developed in terrestrial animals, which is associated with the loss of the locomotor function of the tail during the transition of animals to a terrestrial lifestyle.

The axial skeleton is subject to the following laws of body structure, which ensure the mobility of the animal. These include :

1) Bipolarity (uniaxiality) is expressed in the fact that all parts of the axial skeleton are located on the same axis of the body, with the skull on the cranial pole and the tail on the opposite pole. The sign of uniaxiality allows us to establish two directions in the animal’s body: cranial - towards the head and caudal - towards the tail.

2) Bilaterality (bilateral symmetry) is characterized by the fact that the skeleton, like the torso, can be divided by the sagittal, medial plane into two symmetrical halves (right and left), in accordance with this the vertebrae will be divided into two symmetrical halves. Bilaterality (antimerism) makes it possible to distinguish lateral (lateral, external) and medial (internal) directions on the animal’s body.

3) Segmentation (metamerism) lies in the fact that the body can be divided by segmental planes into a certain number of relatively identical metamers - segments. Metameres follow an axis from front to back. On the skeleton, such metameres are vertebrae with ribs.

4) Tetrapodium is the presence of 4 limbs (2 thoracic and 2 pelvic)

5) And the last regularity is, due to the force of gravity, the location in the spinal canal of the neural tube, and below it the intestinal tube with all its derivatives. In this regard, the dorsal direction is marked on the body - towards the back and the ventral direction - towards the abdomen.

Peripheral skeleton represented by two pairs of limbs: thoracic and pelvic. In the skeleton of the limbs there is only one pattern - bilaterality (antimerism). The limbs are paired, there are left and right limbs. The remaining elements are asymmetrical. On the limbs there are girdles (thoracic and pelvic) and a skeleton of free limbs.

Using a belt, the free limb is attached to the spinal column. Initially, the limb girdles had three pairs of bones: a scapula, a clavicle and a coracoid bone (all preserved in birds); in animals, only one scapula remained; from the coracoid bone, only a process on the tubercle of the scapula on the medial side was preserved; rudiments of the clavicle are present in predators (dogs) and cat). In the pelvic girdle, all three bones (iliac, pubic and ischial) are well developed, which grow together.

The skeleton of the free limbs has three links. The first link (stilopodium) has one ray (Greek stilos - column, podos - leg): on thoracic limb- this is the humerus, on the pelvic bone - the femur. The second links (zeugopodium) are represented by two rays (zeugos - pair): on the thoracic limb there are the radius and ulna bones (bones of the forearm), on the pelvic limb there are the tibia and fibula bones (tibia bones). The third links (autipodium) form: on the thoracic limb - the hand, on the pelvic limb - the foot. They distinguish between basipodia (the upper section - the bones of the wrist and, accordingly, the tarsus), metapodium (middle - the bones of the metacarpus and metatarsus) and acropodium (the outermost section - the phalanges of the fingers).

SKELETAL PHYLOGENESIS

In vertebrate phylogenesis, the skeleton develops in two directions: external and internal.

The exoskeleton performs a protective function, is characteristic of lower vertebrates and is located on the body in the form of scales or shell (turtle, armadillo). In higher vertebrates, the external skeleton disappears, but its individual elements remain, changing their purpose and location, becoming the covering bones of the skull and, located under the skin, connected with the internal skeleton. In phylo-ontogenesis, such bones go through only two stages of development (connective tissue and bone) and are called primary. They are not able to regenerate; if the skull bones are injured, they are forced to be replaced with artificial plates.

The internal skeleton performs mainly a supporting function. During development, under the influence of biomechanical load, it constantly changes. If we consider invertebrate animals, then their internal skeleton has the form of partitions to which muscles are attached.

In primitive chordates animals (lancelet ), Along with the septa, an axis appears - the notochord (cellular cord), covered with connective tissue membranes.

U cartilaginous fish(sharks, rays) cartilaginous arches are formed segmentally around the notochord, which subsequently form vertebrae. The cartilaginous vertebrae, connecting to each other, form the spinal column, and the ribs are attached to it ventrally. Thus, the notochord remains in the form of nuclei pulposus between the vertebral bodies. The skull is formed at the cranial end of the body and, together with the vertebral column, participates in the formation of the axial skeleton. Subsequently, the cartilaginous skeleton is replaced by a bone one, less flexible, but more durable.

U bony fish the axial skeleton is built from stronger, coarse-fibrous bone tissue, which is characterized by the presence of mineral salts and a random arrangement of collagen (ossein) fibers in the amorphous component.

With the transition of animals to a terrestrial lifestyle, amphibians a new part of the skeleton is formed - the skeleton of the limbs. As a result of this, in terrestrial animals, in addition to the axial skeleton, a peripheral skeleton (the skeleton of the limbs) is also formed. In amphibians, as well as in bony fish, the skeleton is built of coarse fibrous bone tissue, but in more highly organized terrestrial animals (reptiles, birds and mammals) the skeleton is already built from lamellar bone tissue, consisting of bone plates containing collagen (ossein) fibers arranged in an orderly manner.

Thus, the internal skeleton of vertebrates goes through three stages of development in phylogenesis: connective tissue (membranous), cartilaginous and bone. The bones of the internal skeleton that go through all these three stages are called secondary (primordial).

ONTOGENESIS OF THE SKELETON

In accordance with the basic biogenetic law of Baer and E. Haeckel, in ontogenesis the skeleton also goes through three stages of development: membranous (connective tissue), cartilaginous and bone.

At the earliest stage of embryonic development, the supporting part of its body is dense connective tissue, which forms the membranous skeleton. Then a notochord appears in the embryo, and around it, first a cartilaginous, and later a bony spinal column and skull, and then limbs begin to form.

In the prefetal period, the entire skeleton, with the exception of the primary integumentary bones of the skull, is cartilaginous and makes up about 50% of the body weight. Each cartilage has the shape of a future bone and is covered with perichondrium (a dense connective tissue membrane). During this period, ossification of the skeleton begins, i.e. formation of bone tissue in place of cartilage. Ossification or ossification (Latin os - bone, facio - do) occurs both from the outer surface (perichondral ossification) and from the inside (enchondral ossification). In place of the cartilage, coarse fibrous bone tissue is formed. As a result of this, in fruits the skeleton is built of coarse fibrous bone tissue.

Only in the neonatal period is coarse fibrous bone tissue replaced by more advanced lamellar bone tissue. During this period it is required Special attention to newborns, since their skeleton is not yet strong. As for the notochord, its remains are located in the center of the intervertebral discs in the form of nuclei pulposus. During this period, special attention should be paid to the integumentary bones of the skull (occipital, parietal and temporal), as they bypass the cartilaginous stage. Between them in ontogenesis, significant connective tissue spaces called fontanelles (fonticulus) are formed; only in old age do they completely undergo ossification (endesmal ossification).



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, the ethmoid bone appears. 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; nerve exit holes, 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 (radius 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 an articular surface for 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 outwards ear canal. The anterior part of the floor of the skull is represented by the secondary hard palate, characteristic of mammals, 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 characteristics. 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. The dentary 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. The lower part of the hyoid arch (hyoid and copula), as well as the first branchial arch in mammals, is 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 spine 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).

First two cervical vertebrae in mammals, like all amniotes, they 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 - big 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 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 the 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 paired limbs of mammals has everything typical signs 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 by a patella characteristic of mammals, 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 various conditions and their adaptation to various types of movement, the described type of limbs in some representatives undergoes changes. 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).

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 the organs of the chest and abdominal cavity, brain, nerves, and blood vessels from external influences.

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 support them in such a position that the leaf blades are illuminated as best as possible 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 an irregular shape and very 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.

Skeleton(from the Greek “skeleton” - dried) are structures of various structures and origins that ensure the preservation of the shape of the animal’s body, as well as support and protection for internal organs. In addition, they are attached to individual components of the skeleton. muscles, ensuring the movement of the animal - so the skeleton is an important functional subdivision of the musculoskeletal system. Vertebrates, unlike most invertebrates, have endoskeleton- i.e. their supporting structures are located not on the surface, but in the deep parts of the body.

The prototype of the vertebrate skeleton - and also the only skeletal structure in lower chordates - is chord, a dense cord of cells of mesodermal origin, stretching along the dorsal (dorsal) side through the entire body, from head to tail. In higher chordates - vertebrates- the notochord is preserved only at the embryonic stage of development, being replaced in adulthood by cartilaginous and bone tissues formed in ontogenesis from mesenchyme, i.e. embryonic connective tissue is predominantly of mesodermal origin. Initially, skeletal elements are formed from cartilage; however, now a cartilaginous skeleton is observed only in lower groups of vertebrates ( lampreys, hagfish, cartilaginous fish and some others). In higher vertebrates, cartilaginous structures are observed mainly in the embryonic stage of development and in childhood; in adulthood, their skeleton is built for the most part from bones.

Anatomically, the vertebrate skeleton is formed by many elements that have different structure, shape, origin and location in the animal's body. These skeletal elements (cartilage or bones) are connected to each other or immovable ( synarthrosis) or movable ( joints) joints; the latter option ensures the movement of body parts relative to each other and the entire body of the animal in the surrounding space. With all the diversity, the skeletal elements of various groups Vertebrates can be grouped into several divisions.

Integumentary skeleton

The integumentary skeleton is a collection of bone elements located in skin animal; these elements are initially formed from bone tissue and do not have a cartilaginous stage of development. The skin of modern vertebrates usually does not contain any bone elements, but in many extinct forms the body was partially or completely enclosed in a bony shell; in addition, some bones are of integumentary origin skulls And limb belts.

Modern lampreys And mikisny do not have any bony shell, but many ancient aquatic vertebrates (for example, armored fish) were completely clad in powerful armor; The overwhelming majority of modern fish also have a protective layer on top of the skin made of bony scales of various shapes and structures; the covering bones also include elements of the operculum.

Terrestrial four-legged vertebrates initially also had a complete bone cover of plates and scales; subsequently, some of its components became part of the skull, jaws, and limb girdles, while others were lost. The skin of these vertebrates, however, retained the ability to form bone, so that some of their representatives secondarily acquired protective scales or plates - for example, abdominal ribs crocodiles, shell turtles And armadillos.

Internal skeleton

Bird skeleton

Read more about Bird Skeleton

Mammal skeleton

More details o Mammal skeleton

Human skeleton

More details o Human skeleton

Unlike the integumentary skeleton, the internal elements are formed in the deep parts of the body and are initially formed by cartilage; as already noted, in lower representatives it partially or completely retains the cartilaginous composition, while in higher representatives, in the process of ontogenesis, cartilage is gradually replaced by bone.

Spine

Spinal column, formed by many vertebrae, - essential element so-called axial skeleton, historically formed around the notochord, although the notochord itself is reduced in adulthood, remaining only in fish, primitive amphibians And reptiles, being strongly compressed within the vertebrae and expanding between them; in most terrestrial vertebrates, the remains of the notochord are only gelatinous formations in intervertebral discs . Individual vertebrae have different structures in different groups of vertebrates; in addition, within the same organism, the vertebrae are also heterogeneous, which makes it possible to distinguish several sections of the spine. The spine of fish is most simply structured - only the trunk and caudal sections are clearly distinguished; in the course of further evolution, the thoracic, cervical, lumbar and sacral regions became separated; Each group of vertebrates has its own special set of spinal sections.

The axial skeleton includes ribs, first appearing in cartilaginous fish and representing elongated cartilaginous or bony formations that serve mainly for the attachment of muscles; Different groups of vertebrates have ribs of different shapes, sizes and origins, connected to the vertebrae of one or more parts of the spine. On the ventral (ventral) side, the ribs can join sternum, thus forming chest.

Scull

Skeleton of the head - scull- is a very complex formation, consisting of many cartilaginous or bone elements with different structures and origins: here there is a combination of both internal and integumentary bones fused with them. In general terms, the composition of the vertebrate skull can be divided into four components:

• brain box- in fact, it is a continuation of the axial skeleton, formed along the back, lower and lateral sides of the brain from the internal and partially integumentary bones. The occipital region also contains foramen magnum, through which the spinal cord passes, and also condyles to connect to the first vertebra.
• skull roof- bone elements covering the brain from above, in front and from the sides, as well as forming the structures of the nose, eye sockets, temporal region, upper jaw, and formed exclusively by integumentary bones.
• palatal complex- elements that form the primary and secondary palate and are formed by the internal and integumentary bones.
• visceral skeleton- cartilaginous or bone elements that initially form around oral cavity and pharynx, but originating from the mesenchyme of endodermal origin. The lower chordates present gill arches, the front of which are transformed into jaws; in the higher ones they are supplemented by the integumentary bones of the lower jaw and hyoid region, the remains of the former gill arches are transformed into the bones of the middle ear or into cartilage not related to the skeleton itself larynx.

Skeleton of limb belts

Limb belts- these are cartilaginous or bone formations designed to connect the limbs themselves to the body. Accordingly with the limbs, they distinguish shoulder girdle, or the belt of the forelimbs, and pelvic girdle, or the belt of the hind limbs. The composition and structure of the limb girdles vary among different groups of vertebrates, but some general patterns are observed.

• shoulder girdle consists of two parts - integumentary and internal origin. The integumentary ones include collarbone and some other bones that provide connection between the forelimb and the spine, and in fish, also with the skull. The internal bones of the shoulder girdle are represented in higher vertebrates spatula- a bone directly connected to the forelimb and serving for muscle attachment.
• pelvic girdle- a purely endoskeletal formation that serves to attach the muscles of the hind limb. In fish, the pelvic girdle is a simple element that is in no way connected with the axial skeleton; in terrestrial vertebrates, on the contrary, it is attached to the spine and consists of clearly distinguishable three pairs of bones.

Limb skeleton

Free limbs vertebrates that serve as a means of transportation have some variations among different groups. So, ray-finned fish have paired fins(thoracic and abdominal), built according to the fold principle; these limbs have practically no internal skeleton, supported by rays of integumentary origin. Fins of the Ancients lobe-finned fish, on the contrary, demonstrate a typical three-segmented structure, in which the segment closest to the body is formed by a single element, the middle segment by two elements, and the distal segment by many small bones arranged in the form of a blade. Terrestrial vertebrates inherit a similar pattern, and in the third (distal) segment, in general, only five rays remain - this is how a typical five-fingered limb is formed, consisting of shoulder, forearms And brushes(for the front) or from hips, shins And feet(for the back).

Spinal column: structure, development, specific features

According to its development, the spinal column (columna vertebralis) is formed around the spinal cord, forming a bone container for it. In addition to protecting the spinal cord, the spinal column also performs other functions in the body. important functions: is a support for the organs and tissues of the body, supports the head, participates in the formation of the walls of the chest, abdominal cavities and pelvis.

Spinal column(columna vertebralis) consists of individual elements - vertebrae (vertebra). Each vertebra has: a body (corpus vertebrae), a head (caput vertebrae), a fossa (fossa vertebrae), a ventral crest (crista ventralis), an arch (arcus vertebrae), and between the arch and the body a vertebral foramen (foramen vertebrae) is formed. All the vertebral foramina together form spinal canal(canalis vertebralis) for the spinal cord, and the caudal and cranial vertebral notches (incisures caudalis et cranialis) form the intervertebral foramen (foramen intervertebrale) for nerves and vessels. Along the edges of the arches protrude the cranial and caudal articular processes (processus articularis cranialis et caudalis), which serve to articulate the vertebrae with each other. The spinous process (processus spinosus) protrudes - anchoring muscles and ligaments.

The spinal column is divided into cervical, thoracic, lumbar, sacral and caudal regions. The transverse processes (processus transversus) in the thoracic region are needed for articulation of the vertebrae with the ribs, and the transverse costal, mastoid and spinous processes (processus costo-transversarium, mamillaris, spinosus) - for the attachment of muscles.

The number of vertebrae in each section is different and depends on the species characteristics of the animal. Thus, in the cervical region of most mammals (except the sloth and manatee) there are 7 vertebrae. They are divided into: 1st - atlas, 2nd - epistrophe, 3rd, 4th, 5th - typical, 6th, 7th.

· 1st(atlas - atlas), consists of two arches (arcus dorsalis et ventralis), on them, respectively, there are tubercles (tuberculum dorsale et ventrale). The transverse processes form the wings of the atlas (ala atlantis). Under the wing there is a fossa atlas (fossa atlantis), on the wings there are two pairs of openings for blood vessels and nerves - alar (foramen alare) and intervertebral (foramen intervertebrale), there are cranial and caudal articular fossae (fovea articularis cranialis et caudalis). FEATURES: there are no transverse holes on the atlas of the domestic bull.

· 2nd(axial epistrophy - axis), characterized by the presence of a tooth (dens) instead of the vertebral head and a ridge (crista dorsalis) instead of the spinous process, also a single transverse process (processus transversus).

· 3rd, 4th, 5th- typical. – their transverse processes have fused with the costal ones, forming the transverse costal processes (processus costo-transversarium), and the spinous processes are inclined towards the head.

· 6th and 7th vertebrae - differ from the rest in shape and are atypical. 6th – instead of a ventral ridge, it has a massive ventral plate (lamina ventralis). 7th - does not have a transverse foramen, but has caudal costal fossae (fovea costalis caudalis) on the vertebral body.

In the thoracic region of vertebrates, cattle and dogs have 13 vertebrae, pigs have 14-17, and horses have 18. Thoracic vertebrae(vertebrae thoracicae) together with the ribs and sternum form the chest. The vertebrae of this section have caudal and cranial costal fossae (fovea costalis caudalis et cranialis), costal facets on the transverse processes (fovea costalis processus transversalis). The spinous process (processus spinosus) is inclined back towards the tail. The spinous processes of the vertebrae from the 2nd to the 9th form the base of the withers (regio interscapularis). The spinous process of the 13th (12th in a pig, 16th in a horse, 11th in a dog) vertebra stands vertically - diaphragmatic. The mastoid processes (processus mamillaris) are located on the transverse processes (processus transversus).

IN lumbar region The spine in cattle and horses has 6 vertebrae, in pigs and dogs there are 7. Lumbar vertebrae (vertebrae lumbales), characterized by the presence of long, flat transverse processes and well-developed articular processes. (In the domestic bull:) vertebral bodies with a waist-like interception, transverse processes with sharp, uneven edges and curved forward towards the head. The spinous processes stand vertically. The cranial articular processes form semicylindrical bushings, and the caudal ones form the same blocks.

IN sacral region The vertebrae of the spine (vertebrae sacrales) fuse into one bone - the sacrum (os sacrum), which consists of 5 vertebrae in cattle and horses, 4 in pigs, and 3 in dogs.

The spinous processes have merged into the medial sacral crest (crista sacralis mediana), and there are no interaricular foramina. The intervertebral notches formed 4 pairs of dorsal and ventral sacral foramina (foramina sacralia dorsalia et ventralia). The transverse processes have merged - jagged lateral parts (partes lateralis). The first two transverse processes formed the wings of the sacrum (ala sacralis). On the wings, the auricular part (facies auricularis) is located dorsally, and the ventral part is the pelvic part (facies pelvina). On the vent. Almost visible transverse lines(lineae transversae), the vascular groove also passes here. The head ventrally forms the promontory of the sacrum (promontorium). There is also a sacral canal (canalis sacralis).

The caudal spine is the most variable in the number of vertebrae, of which there are 20-23 in dogs, 20-25 in pigs, 18-20 in cattle, and 18-20 in horses. In the structure of the caudal vertebrae (vertebrae caudales (coccygeae)), a gradual reduction of the arch is observed. On the ventral side from 2 to 13, hemal processes (processus hemalis) are well developed.