Practical work “Features of the internal structure of the sand lizard. The structure of a lizard The structure of the internal organs of a lizard

Reptiles are the first terrestrial vertebrates; some species again switched to an aquatic lifestyle.

The eggs of reptiles are large, rich in yolk and protein, covered with a dense parchment-like shell, and develop on land or in the mother’s oviducts. There is no aquatic larva. A young animal born from an egg differs from adults only in size.

Dry skin is covered with horny scales and scutes.

1. Nostrils
2. Eyes
3. Head
4. Torso
5. Eardrum
6. Scales
7. Claws
8. Forelimb
9. Hind limb
10. Tail

Internal structure of a lizard

Digestive system

Mouth, oral cavity, pharynx, stomach, digestive glands, pancreas, liver, small and large intestines, cloaca - these are the parts of the digestive system of reptiles.

In the mouth, saliva moistens food, making it easier to move through the esophagus. In the stomach, under the influence of gastric juice, protein foods are digested in an acidic environment. The ducts of the gallbladder, liver and pancreas open into the intestine. Here food digestion is completed and nutrients are absorbed into the blood. Undigested food remains are expelled through the cloaca.

Excretory system

The excretory organs are the kidneys, ureters and bladder.

Skeleton

The skeleton is completely bony. The spine is divided into five sections: cervical, thoracic, lumbar, sacral and caudal. The head is mobile due to the elongation of the neck and the presence of two specialized cervical vertebrae.

1. Scull
2. Spatula
3. Bones of the forelimb
4. Spine
5. Ribs
6. Pelvic bones
7. Bones of the hind limb

The cervical region consists of several vertebrae, with the first two allowing the head to turn in any direction. And this is extremely important for orientation using the senses located on the head.

The thoracic region fixes the shoulder girdle through the chest and provides support for the forelimbs. The lumbar region provides curves to the torso that aid in movement. The powerful sacral section already consists of two vertebrae and the belt of the hind limbs is numb. The long tail provides balancing movements of the tail.

Since the oral cavity no longer participates in gas exchange, the jaws have become elongated, more suitable for their main function - capturing food. Stronger jaw muscles attached to the new projections on the skull allowed for a significantly expanded diet.

Organ systems

Respiratory

Breathing is only pulmonary. The breathing mechanism is of the suction type (breathing occurs by changing the volume of the chest), more advanced than that of amphibians. Conducting airways (larynx, trachea, bronchi) are developed. The inner walls and septa of the lungs have a cellular structure.

Blood

The heart is three-chambered, consisting of two atria and one ventricle. The ventricle has an incomplete septum. The systemic and pulmonary circulations are not completely separated, but the venous and arterial flows are more clearly separated, so the body of reptiles is supplied with more oxygenated blood.

The right atrium receives venous blood from all organs of the body, and the left atrium receives arterial blood from the lungs. When the ventricle contracts, its incomplete septum reaches the dorsal wall and separates the right and left halves. From the left half of the ventricle, arterial blood enters the vessels of the brain and the anterior part of the body; from the right half, venous blood goes to the pulmonary artery and further to the lungs. The trunk region receives mixed blood from both halves of the ventricle.

Nervous

The brain is more developed, especially the forebrain hemispheres (responsible for complex instincts), the optic lobes and the cerebellum (coordinator of movements).

Sense organs

Sense organs are more complex. The reptile's eyes distinguish between moving and stationary objects. The lens in the eyes can not only move, but also change its curvature. Lizards have movable eyelids. In the olfactory organs, part of the nasopharyngeal passage is divided into olfactory and respiratory sections.

The internal nostrils open closer to the throat, so reptiles can breathe freely when they have food in their mouths.

Fertilization

Life appeared in water. Metabolic reactions occur in aqueous solutions. Water makes up the largest part of any organism. Individual development of the body requires significant amounts of water. Finally, without water, sperm movement and egg fertilization are impossible. That is why even in amphibians, fertilization and development are strongly associated with the aquatic environment. Overcoming this connection by reptiles is a major breakthrough in evolution.

The transition to reproduction on land was possible only for animals capable of internal fertilization.

Male reptiles have a special organ in the form of a permanent or temporary protrusion, with the help of which seminal fluid from the testes is introduced into the female’s genital tract. This helps protect the sperm from drying out and allows them to move. To meet them, eggs formed in the ovaries descend through the oviduct. There, in the oviduct, the fusion of gametes occurs.

Development

A fertilized egg is a large spherical yolk with a spot of an embryo on it. Descending along the oviduct, the egg is surrounded by egg membranes, of which in reptiles the parchment membrane is the most pronounced. It replaces the mucous membrane of amphibian eggs and protects the egg from external influences on land.

In May - June, the female lays 6-16 eggs in a shallow hole or burrow. The eggs are covered with a soft, fibrous, leathery shell that protects them from drying out. Eggs have a lot of yolk, the white shell is poorly developed. Already at the beginning of the development of the embryo, an extraembryonic bubble is formed from its tissues, which gradually surrounds the embryo on all sides. The embryo, along with the yolk, is suspended inside the egg. The outer shell of the bladder - serosa - creates antimicrobial protection. The inner membrane - the amnion - limits the amniotic cavity, which is filled with fluid. It replaces the embryo with a pool of water: it protects against tremors.

Cut off from the outside world, the fetus could suffocate and be poisoned by its own secretions. These problems are solved by another bladder - the allantois, which is formed from the hindgut and grows into the first bladder. Allantois accepts and isolates all the products of the embryo's excretion, and returns water back. Blood vessels develop in the walls of the allantois, which approach the surface of the egg and ensure the exchange of gases through the membranes of the egg. Thus, the allantois simultaneously plays the role of an embryonic organ of excretion and respiration. All development takes place over 50-60 days, after which the young lizard hatches. The young cub is ready to live on land. It differs from an adult only in its smaller size and underdeveloped reproductive system.

Regeneration

Various birds, small animals and snakes feed on lizards. If the pursuer manages to grab the lizard by the tail, then part of it is thrown away, which saves it from death.

Dropping the tail is a reflex response to pain; it is carried out by breaking the middle of one of the vertebrae. The muscles around the wound contract and there is no bleeding. Later, the tail grows back - regenerates.

Axial skeleton. The differentiation of the axial skeleton, or spine, into sections is expressed much more clearly in reptiles than in amphibians. The cervical region is always composed of several vertebrae, of which the two anterior ones have a special structure. The first cervical vertebra is called the atlas or atlas. It lacks a vertebral body and has the shape of a ring divided into two parts. On the lower anterior surface of this vertebra there is an articular cavity that movably connects with the condyle of the skull. The second cervical vertebra, the epistropheus, has a large odontoid process in front, which represents the body of the first cervical vertebra, fused with the epistropheus. The odontoid process fits freely into the lower opening of the atlas. This structure of the first cervical vertebrae provides greater mobility of the head. The remaining cervical vertebrae have the usual structure; many of them bear short cervical ribs.

Monitor lizard vertebrae.
A - atlas; B - epistrophy; B - thoracic vertebra;
G - longitudinal section of the thoracic vertebra:
1 - odontoid process of epistrophy, 2 - vertebral body, 3 - upper arch,
4 - spinous process, 5 - canal for the spinal cord, 6 - anterior articular process,
7 - posterior articular process

The thoracic and lumbar sections are not clearly distinguished and are usually considered as a single section. The thoracic region itself is considered to be that part of the spine in which the ribs extending from the vertebrae are articulated with the lower end to the sternum. The lumbar vertebrae bear ribs that do not reach the sternum. The vertebral bodies are concave in front and convex in back; such vertebrae are called procoelous. The upper arches rise above the vertebral body, ending in the spinous process. The spinal cord is located in the canal formed by the superior arches.

From the anterior and posterior sections of the base of the upper arches, the anterior and posterior articular processes depart, respectively. These paired processes connect to the articular processes of adjacent vertebrae and contribute to greater strength of the spine during bending. On the sides of the vertebral body (near the base of the upper arches) there are small depressions to which the ribs are attached.

The sacral section consists of two vertebrae, which are characterized by powerfully developed transverse processes; they are joined by the pelvic bones. The caudal region is represented by numerous vertebrae, gradually decreasing in size.

This structure of the spine is typical for the class of reptiles, but in some groups it undergoes secondary changes. In particular, in snakes, due to the reduction of paired limbs and the emergence of a different type of movement - crawling on the belly by bending the body - the spine is clearly divided only into the trunk and caudal sections. All trunk vertebrae have movable ribs, the lower ends of which are free (snakes have no sternum) and rest against the ventral horny scutes.

Swamp turtle skeleton.
A - carapace; B - plastron:
1 - trunk section of the spinal column, 2 - costal plates,
3 - marginal plates, 4 - coracoid, 5 - scapula, 6 - ilium,
7 - pubic bone, 8 - ischium

In turtles, the axial skeleton takes part in the formation of the bone base of their shell. The upper shield of the shell - the carapace - is composed of several rows of bone plates. The middle (unpaired) row of these plates is formed by the fusion of the expanded and flattened spinous and transverse processes of the trunk vertebrae with the skin bones; On the sides of the middle row there are paired rows of bone plates fused with expanded ribs. The edge of the carapace is formed by bone plates of integumentary origin. Thus, the torso spine of turtles is motionless and firmly fused with the dorsal shield of the shell. The cervical and caudal sections of the spine are mobile. In this case, the anterior cervical vertebrae are opisthocoelous (the vertebral body is convex in front, concave in the back), the posterior ones are produral, and between these two groups there is one vertebra, the body of which has a convex surface both in front and behind.

Scull. Compared to amphibians, the skull of reptiles is characterized by much more complete ossification. A certain amount of cartilage is preserved only in the olfactory capsule and in the auditory region. The axial and visceral sections of the skull are embryonically formed separately, but in adult animals they form a single formation. The skull includes both cartilaginous (replacement, or primary) and numerous dermal (integumentary, or secondary) bones. It is convenient to use the skull of a large lizard - the monitor lizard - as the main object for study.

Monitor lizard skull.
A - side; B - bottom; B - from above; G - rear:
1 - main occipital bone, 2 - lateral occipital bone,
3 - superior occipital bone, 4 - foramen magnum,
5 - occipital condyle, 6 - anterior auricular bone,
7 - main sphenoid bone, 8 - vomer, 9 - parietal bone,
10 - frontal bone, 11 - nasal bone, 12 - prefrontal bone,
13 - preorbital bone, 14 - lacrimal bone, 15 - superior temporal fossa,
16 - postfrontal bone, 17 - squamosal bone, 18 - premaxillary bone,
19 - maxillary bone, 20 - zygomatic bone, 21 - rupture of the lower temporal arch due to reduction of the quadratozygomatic bone, 22 - quadrate bone,
23 - pterygoid bone, 24 - palatine bone, 25 - superior pterygoid bone,
26 - transverse bone, 27 - surangular bone, 28 - dentary bone, 29 - angular bone,
30 - articular bone, 31 - coronoid bone

Axial skull . In the occipital region of the skull there are all four occipital bones: the main occipital, two lateral occipitals and the superior occipital. These primary bones surround the foramen magnum. The lower and lateral occipital bones together form the only (unlike amphibians) occipital condyle, which movably articulates with the first cervical vertebra - the atlas. The articulation of the head with the neck using only one condyle, in combination with the structural features of the first two cervical vertebrae already discussed, gives the reptile head significant mobility.
In the auditory section, of the cartilaginous bones, only the paired anterior auricular bone retains its independence, while the superior auricular bones are fused with the upper occipital bone, and the posterior auricular bones are fused with the lateral occipital bones.

The interorbital septum in reptiles is thin, membranous, and only in crocodiles and lizards does it have separate small ossifications, apparently corresponding to the oculo-sphenoid bones. The olfactory capsule has no ossifications.

At the base of the skull in front of the main occipital bone there is a rather large integumentary main sphenoid bone. Its anterior narrow process is homologous to the parasphenoid (parasphenoideum), which is noticeably reduced in reptiles. In the anterior part of the bottom of the skull, under the olfactory region, there is a paired vomer, also of integumentary origin.
The roof of the skull is represented by numerous covering bones, some of which descend downwards and cover the skull from the sides. These include the parietal, frontal and nasal bones. In front of the frontal bones there are usually paired prefrontal and preorbital bones, and under them in the anterior wall of the orbit there are paired lacrimal bones pierced by a narrow canal.

Crocodile skull (Mississippi alligator).
A - from above; B - bottom:
1 - premaxillary bone, 2 - maxillary bone, 3 - zygomatic bone,
4 - quadratozygomatic bone, 5 - quadrate bone, 6 - external nostril,
7 - orbit, 8 - lateral temporal fossa, 9 - superior temporal fossa, 10 - squamosal bone,
11 - postfrontal (postorbital) bone, 12 - parietal bone, 13 - frontal bone,
14 - prefrontal bone, 15 - nasal bone, 16 - lacrimal bone, 17 - palatine bone,
18 - pterygoid bone, 19 - transverse bone,
20 - choanae (internal openings of the nostrils), 21 - occipital condyle

Of the remaining integumentary bones of the axial skull, the bones that take part in the formation of the so-called temporal arches are of particular interest. In the crocodile, there is a hole in the roof of the skull outward from the parietal bone on each side - the superior temporal fossa. Along the outer edge, the superior temporal fossa is bounded by the postfrontal or postorbital squamosal bones. These two bones together make up the superior temporal arch. On the side of the skull behind the orbit are the lateral temporal fossae, bounded externally by the lower temporal arches. Each lower temporal arch is composed of two bones: the zygomatic and the quadratozygomatic. The lower temporal arch connects to the upper jaw: the zygomatic bone grows into the maxillary, and the quadratozygomatic bone grows into the quadrate. This type of skull, like that of a crocodile - with two temporal pits and two temporal arches, is called diapsid (bi-arched).

In the monitor lizard, the upper temporal fossa is limited by the complete upper temporal arch. As part of the lower temporal arch, the quadratozygomatic bone was reduced and only the zygomatic bone was preserved; As a result, the lateral temporal fossae are not closed from the outside and remain open. Therefore, the skull of the monitor lizard can be considered as a skull of the diapsid type, but with a reduced lower arch. In some other lizards, the superior temporal arch is also partially reduced, and in snakes, both temporal arches are reduced (the postfrontal and squamosal bones are not connected to each other; both temporal fossae remain open on the outside). Thus, snakes and lizards (squamate order, Squamata) according to the structure of the skull belong to the group of diapsid (biarched) reptiles, but are characterized by varying degrees of reduction of the temporal arches.

Swamp turtle skull:
1 - false temporal fossa, 2 - premaxillary bone, 3 - maxillary bone,
4 - zygomatic bone, 5 - quadratozygomatic bone, 6 - quadrate bone,
7 - squamosal bone, 8 - postfrontal bone, 9 - parietal bone,
10 - frontal bone, 11 - prefrontal bone, 12 - upper occipital bone

In the turtle, both temporal fossae are absent, and the side wall of the roof of the skull, delimiting the outside of a large cavity - the so-called false temporal fossa, formed as a notch in the occipital part of the skull, is composed of tightly fused bones: postfrontal, squamosal, zygomatic and quadratozygomatic. This type of skull, devoid of true temporal fossae and the temporal arches limiting them, is called anapsid (arcless).

Visceral skull . In the monitor lizard, the palatoquadrate cartilage ossifies, forming a quadrate bone in the posterior section, to the lower end of which the lower jaw is attached; the upper end of the quadrate is movably articulated with the axial skull. In front of the quadrate bone is the pterygoid bone, and in front of it is the palatine bone, which connects to the maxillary bones and the vomer. All these bones are paired; Of these, only the quadrate bones are of cartilaginous (primary) origin.

The superior pterygoid bone extends upward from the pterygoid bone. This paired bone, connecting the pterygoid and parietal bones, is homologous to the vertical (“ascending”) process of the palatoquadrate cartilage and is characteristic of living reptiles for lizards and hatteria. In addition to the maxillary bones, transverse bones extend from the pterygoid bones, which in their anterior part are attached to the maxillary bones. The secondary upper jaw is represented by the premaxillary and maxillary bones. The lower jaw consists of a primary articular bone and integumentary bones: the dental, angular, surangular, coronoid and, sometimes, several other small bones.

On the premaxillary, jaw and dental bones of reptiles (except turtles) there are simple conical, sometimes slightly curved back teeth, which grow to the edge of the corresponding bone.
The hyoid arch, like that of amphibians, has completely lost its suspension function. The upper element of the hyoid arch (hyomandibular) is part of the middle ear in the form of a rod-shaped auditory ossicle - stapes (stapesseucolumella), and the rest of it, together with the remains of the anterior branchial arches, forms the hyoid apparatus.
The described structure of the visceral skull is generally typical for all reptiles. But in some groups there are deviations from this scheme, associated mainly with the specific biology of these groups.

Poisonous snake skull:
1 - premaxillary bone, 2 - maxillary bone. 3 - palatine bone,
4 - pterygoid bone, 5 - transverse bone, 6 - quadrate bone, 7 - squamosal bone,
8 - postfrontal bone, 9 - poisonous tooth, 10 - frontal bone, 11 - nasal bone,
12 - dentary bone. 13 - angular bone, 14 - articular bone

In snakes, not only the quadrate bones are very mobile, but also the scaly bones connected to them, as well as the pterygoid and palatine bones. The last two bear sharp teeth. The transverse bones in snakes serve as levers, transmitting the movements of the pterygoid bones to the maxillary bones, which in turn are very mobile. This entire system of movably articulated bones not only contributes to an extremely wide opening of the mouth, but also ensures independent movements of the right and left halves of the jaw apparatus when pushing prey into the pharynx with alternate interception. This allows snakes to swallow relatively very large (exceeding the thickness of the snake's body) prey. Poisonous snakes have movably attached sharp, backward-curved poisonous teeth on their maxillary bones, which have an internal channel or groove on the front surface, through which, when bitten, venom flows into the wound from the poisonous glands located at the base of the tooth.

The skull of crocodiles is characterized by the fact that the teeth do not grow to the edge of the dental, premaxillary and maxillary bones, as in other reptiles, but sit in special recesses (sockets, or alveoli) of these bones - thecodont teeth. Another feature of the visceral skull of crocodiles is the secondary hard palate, which separates the oral cavity from the nasopharyngeal passage. The palatine processes of the premaxillary and maxillary bones, as well as the palatine and pterygoid bones, take part in the formation of the secondary hard palate. Thanks to the formation of the hard palate, the secondary choanae are carried back and located in the pterygoid bones, above the larynx. The formation of a secondary hard palate is associated with the nature of the lifestyle of crocodiles: direct contact of the larynx with the choanae opens up the possibility of uninterrupted breathing when eating and when the crocodile rests in shallow water, exposing the nostrils located on the elevations from the water, while the oral cavity is filled with water.

Paired limbs and their belts. The shoulder girdle of reptiles consists of typical bones: the scapula located more dorsally and the coracoid facing the ventral side. Both of these bones take part in the formation of the articular fossa for the attachment of the forelimb. Dorsal to the scapula there is a wide, flattened suprascapular cartilage, and in front of the coracoid there is a cartilaginous procoracoid. There is a well-developed sternum, to which several ribs are articulated. Thus, unlike amphibians, reptiles develop a rib cage and the shoulder girdle is supported in the axial skeleton. On the ventral side of the sternum there is a T-shaped integumentary bone - the episternum, in front of it there are also integumentary bones - the clavicles. The outer ends of the clavicles are attached to the shoulder blades, and the inner ends are fused with the branches of the episternum. The collarbones and episternalum (absent in amphibians) increase the strength of the connection between the right and left parts of the shoulder girdle.

Shoulder girdle of a monitor lizard (bottom view):
1 - scapula, 2 - suprascapular cartilage, 3 - coracoid,
4 - articular cavity for the head of the humerus, 5 - procoracoid cartilage,
6 - sternum, 7 - ribs, 8 - episternum, 9 - clavicle

In snakes, the shoulder girdle is completely reduced, and in turtles, the clavicles and episternum became part of the bones of the abdominal shield of the shell, respectively forming the anterior paired and unpaired bone plates wedged between them.

Pelvic girdle of a monitor lizard (bottom view):
1 - ilium, 2 - pubic bone, 3 - ischium,
4 - acetabulum (articular fossa) for the femoral head,
5 - sacral vertebrae

The pelvic girdle consists of two symmetrical halves, connected along the midline by cartilage.

Each half is made up of three dice; located dorsally iliac, located on the ventral side of the pubis and ischium. All these bones take part in the formation of the articular fossa, to which the hind limb is attached. The pelvis of reptiles is closed: the right and left pubic and ischial bones on the abdominal side are fused to each other.

Limbs of a monitor lizard.
A - front; B - rear:
1 - humerus, 2 - ulna, 3 - radius, 4 - wrist,
5 - metacarpus, 6 - phalanges, 7 - intercarpal joint, 8 - femur,
9 - tibia, 10 - fibula, 11 - patella,
12 - tarsus, 13 - intertarsal joint, 14 - metatarsus

The limbs of reptiles are built according to the typical pattern of the limbs of terrestrial vertebrates. The proximal part of the forelimb is represented by one bone - the humerus, followed by the forearm, consisting of two bones - the ulna and radius. The wrist consists of relatively small bones, usually arranged in two rows; On the side of them there is another bone - a pear-shaped one, taken for the remainder of the sixth finger. The metacarpus is made up of five elongated bones, to which the phalanges of the five fingers are attached. The last phalanges bear claws. The joint that provides mobility of the hand in reptiles does not pass between the bones of the forearm and the proximal row of carpal bones (as in amphibians), but between the proximal and distal rows of carpal bones. This joint is called intercarpal.

In the hind limb, the proximal element - the thigh - articulates with the knee joint with the tibia, consisting of two tibia bones - the tibia and the tibia. Above the front surface of this joint is a small bone - the kneecap. In the tarsus, the proximal row of ossicles fuses or is almost immovably connected to the bones of the leg, and the ossicles of the distal row are also closely connected and partially fused with the metatarsal bones. Due to this, the articular surface here is located not between the lower leg and foot, but between the proximal and distal rows of tarsal bones. This joint is characteristic of reptiles and is called the intertarsal joint. The metatarsus consists of five elongated bones to which the phalanges of the five fingers are attached. The terminal phalanges bear claws.

Determine from Figures 240, 241 what structural features of reptiles contribute to their life on land.
Habitats and lifestyle of reptiles. Reptiles are widespread on all continents except Antarctica. Most of them live in countries with hot and warm climates. These include lizards, turtles, snakes, crocodiles (Fig. 240, 241).

In the central zone of our country, on the edges of forests, in ravines and in gardens, a quick lizard is common. During the day, in sunlit places, she hunts for various insects. A viviparous lizard is found in overgrown clearings and near swamps. It is more active at lower ambient temperatures than the sand lizard. In damp forests (under fallen trees, in rotten stumps, in the forest floor), the legless spindle lizard lives. It feeds on worms, slugs, and insect larvae.

The common grass snake lives along the banks of rivers, ponds and lakes, and in floodplain meadows. Here he catches fish, frogs and swallows them alive. It's a non-venomous snake. Of the poisonous snakes, the common viper lives in the forest and forest-steppe zones. The snake and the viper differ well from each other. The snake has two orange spots on its head. The viper has a zigzag dark stripe along its back.

Among the shifting sands of Central Asia lives one of the largest lizards - the gray monitor lizard (its body length reaches 60 cm).

In the dry foothills, along the slopes of the mountains of Transcaucasia and Central Asia, lives one of the most poisonous snakes - the viper, and in the southern part of Central Asia the sand epha is common (Fig. 259). The Central Asian tortoise lives in clay steppes and sandy deserts (Fig. 260). It feeds on the leaves and stems of various plants.

Features of the external structure. The body of reptiles is elongated (lizards, snakes, crocodiles) or rounded, convex (turtles) (Fig. 239). Their skin is dry. The outer layer of the skin became keratinized and formed horny scales and scutes. This cover protects reptiles well from water loss and thus gives them the opportunity to live in dry places. Turtles and crocodiles, along with horny formations, have bone plates. In turtles they make up the dorsal and ventral shields of the shell (Fig. 242); in crocodiles they are located under the horny plates.

Reptiles molt periodically (Fig. 244).

Reptiles

The legs of reptiles are located on the sides of the body. The body seems to be suspended on them and its belly almost touches the ground. The absence of legs in snakes and legless lizards is a secondary phenomenon.

The eyes of most reptiles have movable eyelids. In snakes and some lizards, they have grown together and turned into a transparent horny covering that protects the eyes from various damages. The lenses of the eyes can not only move forward or backward, but also change their curvature, which allows you to clearly see objects located at different distances. In reptiles, the eardrums are located in recesses of the skin.

Features of the structure of the skeleton. In the spine of reptiles, the cervical, thoracic, lumbar, sacral and caudal sections are clearly distinguished. The cervical region has 8 (in a lizard) or more vertebrae, and the skull articulates with the first cervical vertebra using a single condyle. Thanks to this, reptiles can turn their heads in different directions (Fig. 243).

The ribs articulate with the vertebrae of the thoracic and lumbar regions. In most reptiles, several pairs of ribs connect to the sternum, resulting in the formation of a rib cage, which protects the internal organs and is important in breathing.

In turtles, the ribs are fused to the shell. Therefore, their respiratory movements are carried out by the belt of the forelimbs.

In snakes, all ribs end freely and participate in their movement (Fig. 243). The free arrangement of the ribs and the extensibility of the body walls enable snakes to feed on large prey.

The pelvic bones of reptiles are fused with two vertebrae, which strengthens the girdle of the hind limbs.

IN muscular system In reptiles, intercostal muscles appeared, with the help of which the position of the ribs changes and, as a consequence, the volume of the thoracic cavity of the body changes (the costal method of breathing has developed). In reptiles, neck muscles have formed, and the muscles of the limbs have become more developed than in amphibians.

➊ What animals are classified as reptiles? ➋ What features of the external structure contribute to the life of reptiles in dry places? ➌ What are the features of the skeleton of reptiles and what is their significance? ➍ How is the skeleton of a snake different from the skeleton of a lizard?

Find out this coming summer which reptiles are most common in your area. Make observations of a lizard or snake.

Life of a Komodo dragon

The largest lizard on the planet, also called the “last dragon,” lives on Komodo Island and nearby islands (Indonesia). This is a Komodo dragon.

Its body length reaches three meters, and large individuals weigh up to 130 kg. But sometimes zoologists came across particularly large monitor lizards that weighed more than 160 kg. The color of the “skin” is from gray to black with small light spots - see photo below.

At first glance, this clumsy creature is not capable of running fast. But that's not true. In case of danger or hunting, the Komodo dragon can reach speeds of up to 25 km/h. True, he can make such jerks only for a few seconds. Then he runs out of steam.

In addition, monitor lizards are good swimmers. There is evidence of how this lizard swam across the sea from one island to another. They swim quickly, but after twenty minutes of continuous “swimming” they get tired and exhausted. And if the shore is still very far away, then they drown.

Currently, due to various factors, the population of Komodo dragons has decreased significantly.

Verbal logical diagram "Structure of the skeleton of a lizard"

This was also influenced by human economic activity and the reduction of food on the islands that he inhabits.

In addition to Komodo, it can be found on the territory of the island. Flores, Rinch and many other smaller islands that are part of the Lesser Sunda Archipelago. According to the latest data, about 5 thousand monitor lizards now live in the wild. Now let's talk about the lifestyle of these giant lizards and watch an interesting video.

The life of a monitor lizard on video.

These lizards love warmth, but cannot tolerate the heat of the day. They appear equally often on plains and in forests. During the dry season, they settle closer to bodies of water.

From birth they lead a solitary lifestyle. They don't want to meet each other. They are most active from early morning, from sunrise, until about eleven o'clock. When the sun begins to burn mercilessly towards noon, the Komodo dragon goes into the shade, waiting out the heat until the evening.

But then it begins to get dark - the temperature drops, the sun is approaching sunset, and this lizard again comes out of its shelters. When it gets completely dark, the monitor lizard goes into its lair, which is a huge hole. Adults can dig themselves a “cave” more than 5 meters in length.

Their favorite food is carrion of various animals. Thanks to his sensitive sense of smell, he can smell blood from over 3,000 meters away! Olfactory receptors are located on his tongue, which is very similar to the tongue of a snake (photo).

The monitor lizard feeds on almost all animals that live on the small Sunda islands. Small individuals can feed on insects, birds, turtles, and lizards. He does not disdain small rodents, in particular rats.

But its main food is large ungulates - wild goats, deer, wild boars, buffaloes. There are also many known cases of attacks by these lizards on humans. The number of such attacks increases in dry years, when the monitor lizard lacks food due to drought and approaches populated areas in the hope of preying on domestic animals. Well, people too.

Local residents also dislike this animal because it digs up graves and eats the deceased.

How the Komodo dragon hunts.

This predator has many methods of obtaining food in its arsenal. Sometimes the monitor lizard hunts from some kind of ambush - a stone, tree, bush. Most often, he waits for food in the forests in this way. When any animal approaches him, he hits it with a swing of his tail. After such a blow, the animal loses consciousness or its paws are broken.

The monitor lizard hunts large ungulates differently. Naturally, he cannot cope with a huge buffalo in a fair fight. Moreover, many Komodo dragons die from their horns or hooves.

Therefore, they do not try to engage in a fight with him. They surreptitiously approach him and simply bite him. After this, the buffalo is doomed.

The fact is that the saliva of this predator contains many pathogenic bacteria. These bacteria, entering the blood, cause sepsis (infection) and after a while the bitten person dies.

All this time, the monitor lizard follows on the heels of the victim and waits in the wings. During this time, other lizards will smell the rotting wound and they will also crawl and wait for the victim to die. In the video you can clearly see such a hunt:

In December-January, the mating season begins for Komodo dragons. It is accompanied by mass fights between males for their chosen ones. The fights involve individuals who have reached the age of 10 - it is during this period that the dragons of Komodo Island begin puberty.

The female's pregnancy lasts 120-140 days. When the time comes to lay eggs, the female prepares a nest for herself. In one clutch there are from 10 to 20 large (their weight is 150-200 g) eggs.

For 250-270 days they lie under the strict protection of the female, who tries not to stray far from the nest. When small monitor lizards hatch from eggs, they immediately hide in the trees. This innate instinct saves them from certain death on earth. Young monitor lizards are hunted by snakes, birds, and other animals. Adult monitor lizards also eat them - cannibalism is widespread among this species. Especially in lean years.

They live on trees for about two years. All this time they feed on small birds and insects. Once they reach two years of age, they become too large to live in a tree and are forced to descend to the ground.

According to some reports, these predators can live up to 50 years, since there are no dangerous enemies in nature for large individuals.

Photo and video:

External structure and skeleton of reptiles

External structure Let's look at reptiles using the example of a lizard. Body lizards(as a typical representative of reptiles) is divided into sections: head, torso, tail and two pairs of limbs (Fig. 143, A).

The outside of the body is covered with thick, dry skin. There are no glands in the skin of a lizard. This protects the animal’s body from loss of moisture in a dry environment. Forms in the top layer of skin scales , but not bone, like in fish, but horny , softer. The growth of the reptile's body is accompanied by molting . In this case, the old horny cover exfoliates, bursts, and in lizards comes off in flaps. In snakes it separates, sliding like a stocking from the entire body and is called crawling out .

The head is oval in shape (in snakes it can be triangular) and covered with large horny scutes (they even have special names). In primitive lizards, for example agamas, geckos, the head and body are covered with uniform horny scales.

The mouth has jaws with teeth: with them the lizard grabs and holds prey. A pair of nostrils are visible above the mouth. They are through and allow air into the oral cavity. Inside the nostrils are olfactory organs , with the help of which lizards perceive odors. A long, thin tongue constantly protrudes from the mouths of lizards and snakes, which serves the animal to feel and touch surrounding objects, as well as to perceive their smells. The lizard's eyes are closed moving eyelids .

There is an interception between the head and body - neck . It allows the animal to turn its head in the direction of a sound or moving object, grab prey and deal with it.

The lizard's body is slightly flattened and soft. The tail is long and elastic. It can break off and then be restored - regenerate . Two pairs of legs are widely spaced on the sides of the body, the toes have claws . When the lizard moves creep – touch the ground with their body (hence the name of this class).

Due to the terrestrial lifestyle and the transition to exclusively pulmonary breathing, the body of reptiles is covered with horny scales and lacks glands.

Skeleton. In reptiles, the skeleton is more adapted to life on land than in amphibians (Fig. 143, B).

The head has one protrusion - condyle , which attaches the back of the skull to the spine. This makes the head well mobile when supported by the spine.

The lizard's spine is divided into sections: cervical, trunk, sacral and caudal. There are 7-10 movable vertebrae in the cervical region. The first two stand out - atlas And epistrophy . Their articulation enhances the mobility of the head. They are attached to the trunk vertebrae (16-25) ribs . The anterior true ribs connect to the sternum and form chest .

Skeletal structure of reptiles

It protects the organs located in the chest cavity (esophagus, heart, lungs) from damage and is involved in the breathing mechanism: it expands when inhaling and collapses when exhaling.

In the skeleton of snakes, the ribs are attached to the vertebrae along the entire length of the body part of the spine and are not connected to the sternum (snakes do not have a rib cage). The pelvic girdle is attached to the sacral vertebrae (there are two of them). The skeleton of the belts and free limbs retains the general structure of all terrestrial vertebrates. The limbs of lizards are widely spaced, but there are also legless lizards. Snakes also have no legs. In these cases, reptiles move with the help of powerful muscles attached to the spine and ribs, the ends of which protrude through the skin and cling to uneven ground.

Internal structure and vital functions of reptiles

We will also consider the features of the internal structure and vital activity of reptiles using the example of a lizard.

Nutrition and digestion. The digestive systems of reptiles and amphibians are similar in all main sections (Fig. 144, 145). These are the mouth, pharynx, stomach, intestines. Food gets wet in the mouth saliva , which is typical of terrestrial animals. In the stomach under the influence gastric juice Protein foods are digested in an acidic environment. The ducts of the gallbladder, liver and pancreas open into the intestine. Here food digestion is completed and nutrients are absorbed into the blood.

Lizards eat mainly insects and worms. Snakes hunt voles and mice. Some snakes have special sensory pits on the front of their heads - thermolocators , capable of perceiving heat (infrared radiation) coming from a warm-blooded animal. Venomous snakes kill their prey with venom flowing down the poisonous teeth from poisonous glands located in the walls of the oral cavity.

Respiratory system. Due to the appearance of the cervical spine, the lizard's respiratory tract lengthens, through which air flows from the mouth to the lungs (see Fig. 145). Air is drawn in through the nostrils, into the mouth, then into larynx , then into a long tube - trachea ; the trachea is divided into two even narrower tubes - bronchi , going to the lungs. The lungs of reptiles are more complex than those of amphibians: inside the lung cavity there are many folds where blood vessels branch repeatedly. This increases the surface of their contact with air, enhancing gas exchange.

Circulatory system. Heart three-chamber , with an incomplete septum in the ventricle. Three large vessels emerge from it: the left and right aortic arches and the pulmonary artery (Fig. 146). The two arches of the aorta, bypassing the heart, merge into one common vessel - the dorsal aorta.

Mixed blood flows through the body (like in amphibians), which affects unstable body temperature , depending on the ambient temperature.

The pulmonary arteries carry venous blood from the heart to the lungs for oxygenation. The pulmonary veins carry arterial blood into the left atrium. In the ventricle, the blood is partially mixed, the most oxygen-rich blood goes to the head, mixed - to all organs of the body, saturated with carbon dioxide - to the lungs.

Nervous system. In reptiles, all parts of the brain become more complex and enlarged (Fig. 147) compared to the brain of amphibians. This is manifested in more complex and diverse behavior of reptiles. They form conditioned reflexes faster than fish and amphibians. The forebrain and cerebellum are especially enlarged; the medulla oblongata forms a bend characteristic of all higher vertebrates. In addition to vision and smell, reptiles have a well-developed sense of touch.

Excretory system. In reptiles, the excretory system is the same as in all terrestrial vertebrates. In the excretory organs - the kidneys - the mechanism for returning water to the body is strengthened: it is absorbed by the renal tubules. The end product of metabolism in reptiles is excreted not in the form of liquid urine (as in amphibians), but as uric acid in a pasty state into the cloaca, and then out. Eliminating mushy uric acid from the body does not require as much fluid as liquid urine.

Reproductive organs. These are the testes in males and the ovaries in females (Fig. 148). Fertilization in reptiles is internal. It occurs when the cloaca of a male and female come together. The embryo developing in the fertilized egg, moving along the oviduct, is covered with egg and embryonic membranes. They provide the embryo with water, protect it from drying out and shaking, and are involved in respiration and the release of metabolic products.

Reptiles lay eggs on the ground or in specially prepared depressions (Fig. 149). Some reptiles protect their clutches (for example, crocodiles); others, having laid eggs, leave them (for example, turtles). Sometimes the cubs are carried in the mother's body. In these cases, live birth occurs, for example in vipers and at viviparous lizard.

Annual life cycle. Reptiles are widespread around the globe and are found in different climatic zones. However, being cold-blooded animals with an unstable body temperature, they need external heating from the sun. Therefore, these animals are most numerous in the tropical and subtropical zones of the globe. In the changing seasons, when warm summer is replaced by cold autumn and winter, reptiles, with the onset of unfavorable conditions, go into shelters: holes, caves, under tree roots, under rural houses and forest huts. There the animals fall into stupor - hibernation . In the spring, when the air and soil surface warm up well, reptiles come to the surface and begin an active lifestyle.

Variety of reptiles

There are more than 6 thousand modern species in the class of reptiles. There are groups in the class: Scaly(with suborders of lizards and snakes), Crocodiles And Turtles.

Lizards They are distinguished by a flexible, mobile body and widely spaced legs (Fig. 150). In temperate climates it is kicking And viviparous lizard, and in hot areas it is geckos, agamas, monitor lizards. Known legless lizards - spindle And yellow-bellied. They are distinguished from snakes by their unfused movable eyelids. There are about 3,300 species of lizards in the world. The length of the smallest lizards is about 3.5 cm, the largest - komodo dragon– more than 3 m.

Snakes have no limbs. They move thanks to the powerful muscles of the body and numerous ribs, the ends of which, protruding through the skin, cling to uneven soil. Snakes are distinguished from lizards unblinking gaze since their eyes are covered transparent horny eyelids , and the ability to crawl onto prey like a stocking thanks to its expanding, movable jaws.

Among the snakes there are very large and strong boa constrictors, For example reticulated python, anaconda. Their length reaches 6-10 m. Boa constrictors strangle the caught victim by wrapping their whole body around them. The body length of the smallest snakes is no more than 8 cm.

A lot of poisonous snakes: cobra, viper, viper, rattlesnake, efa. They kill the victim with the venom of their poisonous teeth (Fig. 151). Poisonous snakes are also dangerous to humans. Their bites cause severe illness and even death. In medicine, there are known means to avoid the serious consequences of snake bites.

First aid measures in cases of a poisonous snake bite, the following: applying a splint, calm position of the damaged organ, drinking plenty of warm fluids. The most effective is the administration of anti-snake serum.

The main way to avoid a bite is to be very careful when moving and stopping in places where many poisonous snakes live. Snakes do not like to use poison for defense; they need it as a means of obtaining food. Therefore, when noise approaches, they try to hide.

People have learned to use snake venom for medicinal purposes and use it to treat many diseases.

TO non-venomous snakes relate snakes, snakes, boas. They grab prey with their teeth and then swallow it.

About 2,700 modern species of snakes are known, about a third of them are poisonous.

Crocodiles- large and strong reptiles that live in tropical countries (Fig. 152). Their body length reaches 6 m. They live along the banks of rivers and lakes, hunting for prey in the water. A hidden crocodile grabs a large animal (for example, an antelope) that has come to drink. Crocodiles swim well, using a long, laterally compressed tail and webbed feet. The crocodile's body is completely immersed in water, and only the nostrils and eyes located on the heights of the skull remain above the surface.

Among the crocodiles there are alligators, real crocodiles, gharials, caimans. There are 21 species in the world.

Turtles- the most ancient group among reptiles. Their appearance is very specific: the body is hidden under a powerful hard bony shell (Fig. 153).

Turtles do not molt, so their age can be determined by the dark and light annual stripes on the horny plates of the shell. Although turtles move slowly on land, they are difficult for predators to reach because, when threatened, they pull their head and legs under their shell.

Turtles include land, freshwater and marine species. Their movements in the water are very fast and maneuverable. The largest turtles are sea turtles, for example green (soup) turtle length up to 150 cm and weight up to 400 kg. The largest of the land turtles is Galapagos elephant tortoise, having a shell 150 cm long and weighing up to 400 kg. In total, more than 200 modern species of turtles are known in the world.

Many species of crocodiles and turtles have become very rare; they need protection and are listed in the Red Books.

The meaning of reptiles. Ancient reptiles

The meaning of reptiles. Most lizards and snakes, by eating insects that harm agriculture, rodents and terrestrial mollusks, benefit humans. In some countries in South America, South Asia and Africa, non-venomous snakes are kept instead of cats. In nature, reptiles are woven into a common system food connections : some turtles eat plants, others eat animals (insects, amphibians, reptiles, small animals), and they, in turn, are eaten by other predators - birds of prey and animals.

Sometimes land turtles cause damage to melon fields, and water snakes cause damage to fish farms. Reptiles can spread pathogens to humans and domestic animals.

Poisonous snakes are dangerous with their bites. At the same time, the study of snake venom has led to the creation of valuable medicinal drugs based on them, which people use for diseases of the respiratory organs, heart, and joints.

Large snakes and crocodiles are harvested to make beautiful and durable leather. Sea turtles are hunted for their tasty meat. Because of this, the numbers of many species have sharply declined, and some are on the verge of extinction. Nature reserves have been created for them. Listed in the IUCN Red List Galapagos elephant tortoise, green tortoise, Komodo dragon, Cuban crocodile, hatteria.

Eating plants, insects, amphibians, small animals, reptiles are consumers of ready-made organic substances. Among them there are herbivores and insectivores, but the majority are carnivores (carnivores).

Ancient reptiles. Modern reptiles evolved from ancient amphibians - stegocephali who lived in the middle of the Paleozoic era. The most ancient of reptiles are considered cotylosaurs, who lived 230-250 million years ago. Some features of their organization are preserved in the appearance of turtles.

The heyday of reptiles was the Mesozoic era (250-65 million years ago). In those ancient times, they lived on land and in water, and flew in the air (Fig. 154).

Flying pterodactyls, rhamphorhynchus, pteranodons they looked like giant bats. Their wingspan reached 10-12 m. Lizards resembling dolphins and seals lived in the water. These were ichthyosaurs, plesiosaurs. These groups of ancient reptiles became extinct, leaving no descendants behind.

Among the ancient lizards there were two more groups that played an important role in the emergence of birds and mammals: dinosaurs And animal-like reptiles(Fig. 155).

Dinosaurs were a very diverse group: peaceful (herbivores) and ferocious predators. Some walked on four legs, others only on two hind legs, in an upright position. There are also known very large dinosaurs - more than 30 m long, and small ones - the size of a small lizard. The largest are considered diplodocus(27 m long and weighing about 10 tons), Apatosaurus, Brachiosaurus, Seismosaurus. They lived near bodies of water and stood in the water for a long time, eating aquatic and semi-aquatic vegetation. Some dinosaurs had ridges on their backs that they used to capture solar energy. Scientists suggest that birds originated from one of the groups of dinosaurs.

Animal-like reptiles got their name for their resemblance to animals (see also § 51). Unlike other lizards, their legs were located under the body, lifting it above the ground. Their fangs stood out among their teeth, and fleshy teeth appeared on the front of their heads. lips , and the skin probably had glands.

However, throughout the Mesozoic era, the fate of dinosaurs and beast-like reptiles was different. Dinosaurs were favored by the warm, mild climate of this era, and they dominated everywhere. The beast-like creatures were few in number and invisible. At the end of the Mesozoic era, the ratio of species numbers began to change in favor of animal-like animals.

The extinction of dinosaurs occurred as the planet's climate changed, since at the end of the Mesozoic the long warm period was replaced by low temperatures. At this time, vegetation began to change, and with the beginning of the Cenozoic era, angiosperms began to spread on Earth.

There are many scientifically proven (mountain building and climate change) and alleged reasons for the extinction of dinosaurs. Perhaps a large asteroid passed near the Earth, influencing climate change and the natural environment surrounding dinosaurs.

Did the ancient lizards disappear from the face of the planet without a trace, leaving only monuments in the form of skeletons and prints? In the modern fauna of reptiles there are tuateria which is called living fossil . There is a lot that is archaic in the appearance of this animal: the remains of a shell on the body, the primitive structure of the spine, an additional eye in the parietal part of the head. This reptile lives on small islands off New Zealand and is strictly protected as a living natural monument. Turtles are close to their Mesozoic ancestors.

In some organizational features, crocodiles are close to dinosaurs.

Lizards and snakes also have some similarities with dinosaurs. But in the history of the Earth's vertebrate fauna, they appeared only in the Cenozoic era, when their related groups lost their former greatness.

Evolution

Paleontological finds allow us to conclude that lizards appeared a very long time ago. Already in the Upper Jurassic period, geckos, iguanas, and monitor lizards lived. In the Tertiary period, lizards spread widely, and thanks to the warm climate, their species diversity was great. Of all these species, only a group of giant lizards (Mosasaurus) became extinct, which, along with snakes, originated from monitor lizards and switched to a marine lifestyle at the end of the Cretaceous period.

About 3,000 species of lizards have survived to this day. They make up almost half of all extant reptiles and are taxonomically classified into 22 families.

The systematic position of Amphisbaenia, which has a worm-like body without limbs, remains questionable (snakes or lizards). Their origin is unknown. They probably separated from other lizards in the Lower Cretaceous.

Structure

Typically, lizards have four strong, well-developed limbs. There are, however, numerous species with reduced or completely absent limbs. However, even they have remains of the shoulder and pelvic girdles.

Land-dwelling lizards mostly have short, muscular legs and flat feet. The trend toward smaller limbs is observed primarily in burrowing species.

Tree-dwelling and fast-climbing lizards have long, thin legs, feet and toes with sharp claws. Some species have a prehensile tail.

Geckos have a number of additional adaptations to environmental conditions. On the underside of their toes there are plate-shaped suction pads, allowing geckos to run along vertical walls and even on glass surfaces.

The cervical and dorsal sections of the spine in all lizards consist of 24 vertebrae, from which the ribs extend. In many families of lizards, there are special places in the caudal spine through which, in case of danger, a break occurs, which allows the lizard to cast off its tail (autotomy). Later, complete or partial regeneration of the tail occurs. However, the bony spine is not restored, but only a cartilaginous support grows.

The brain skull of lizards, in contrast to snakes, is not completely closed; there is a rod-shaped bone that rises almost vertically above the pterygoid bone and connects it with the parietal bone.

Among the sense organs, the eyes play the most important role, but many species (for example, geckos) have excellent hearing. Other species are well oriented by smell, perceiving it with the forked tip of the tongue and running it through the Jacobson's organ (a special paired organ for the perception of smells in the palatine notch of amphibians, reptiles and some mammals).

The sand lizard (Lacerta agilis), a scaly reptile from the family of true lizards. The habitat is almost the entire territory and the European part of Russia. The length of the sand lizard reaches more than 220 mm, with relatively short limbs and tail. Let us consider the features of the external and internal structure of the sand lizard.

The lizard's head is pointed in front; it is connected to the body with a short thick neck. At the end of the muzzle there is a pair of nostrils. The lizard's sense of smell is better developed than that of amphibians. The eyes are protected by eyelids. The lizard has a third eyelid - a translucent nictitating membrane, with the help of which the surface of the eye is constantly moistened. Behind the eyes is a rounded eardrum. The lizard's hearing is very sensitive.

From time to time, the lizard sticks out of its mouth a long, thin tongue forked at the end - an organ of touch.

In the limbs of a lizard, the same sections are distinguished as in the limbs of a frog. There are five toes on each foot, there are no membranes between them.

The lizard's entire body is covered with scaly, dry skin. The scales on the face and belly look like large scutes. At the tips of the fingers, the horny cover forms claws. The horny covering of the body prevents the growth of the animal; therefore, the lizard sheds 4-5 times a summer: its keratinized skin exfoliates and comes off in pieces.

Internal structure of a lizard

The lizard does not have skin respiration. She breathes exclusively with her lungs. They have a more complex cellular structure than that of a frog, which increases the surface area for gas exchange in the lungs.

The heart is three-chambered and consists of two atria and a ventricle. Unlike amphibians, the lizard's ventricle is equipped with an incomplete internal septum, which divides it into the right (venous) part and the left (arterial) part.

Despite the greater complexity of the structure of the lizard’s lungs and heart (compared to amphibians), the metabolism in its body is still quite slow and depends on the ambient temperature.

Digestive, excretory and nervous systems lizards are similar in structure to the corresponding amphibian systems. In the brain, the cerebellum, which controls balance and coordination of movements, is more developed than in amphibians, which is associated with the greater mobility of the lizard and the significant variety of its movements.

Lizard Reproduction

In May-June, the female sand lizard lays 5-15 oval eggs, which she buries in a shallow hole or leaves in the same shelter where she spends the night.

The eggs of reptiles are quite large. In the sand lizard, they are oval, up to 1.5 cm long. The egg contains a reserve nutrient - the yolk, due to which the development of the embryo occurs. The outside of the egg is covered with a leathery shell that protects it from drying out. Unlike fish and amphibians, what emerges from the egg is not a larva, but a young lizard that looks like an adult.

Lizard regeneration

Features of the internal structure and vital activity of reptiles are also considered using the example of a lizard.

Nutrition and digestion. The digestive systems of reptiles and amphibians are similar in all main sections (Fig. 143 and 144). These are the mouth, pharynx, stomach, intestines, cloaca.

Rice. 143. Internal structure of a lizard (male): 1 - heart; 2 - trachea; 3 - lungs; 4 - gallbladder; 5 - liver; 6 - stomach; 7 - pancreas; 8 - small intestine; 9 - large intestine; 10 - kidneys; 11 - bladder; 12 - cloacal opening; 13 - testes; 14 - vas deferens

In the mouth, saliva moistens food, making it easier to move through the esophagus. In the stomach, under the influence of gastric juice, protein foods are digested in an acidic environment. The ducts of the gallbladder, liver and pancreas open into the intestine. Here food digestion is completed and nutrients are absorbed into the blood.

Rice. 144. Diagram of the digestive and respiratory systems of a lizard: 7 - mouth; 2 - nostrils; 3 - oral cavity; 4 - pharynx; 5 - esophagus; 6 - trachea; 7 - lung; 8 - liver; 9 - stomach; 10 - pancreas; 11 - small intestine; 12 - large intestine; 13 - cloaca

Lizards eat mainly insects and worms, snakes eat voles, mice, and frogs. Some snakes have special sensitive pits on the front of their heads - thermolocators that can perceive heat (infrared radiation) coming from a warm-blooded animal. Poisonous snakes kill prey with venom from the venom glands (located in the walls of the mouth), which flows down the poisonous teeth.

Respiratory system. Due to the appearance of the cervical spine, the lizard's respiratory tract lengthens, through which air flows from the mouth to the lungs. Air is drawn in through the nostrils, enters the oral cavity, then into the larynx, then into a long tube - the trachea (see Fig. 143). The trachea is divided into narrower tubes - bronchi, which go to the lungs. The lungs of reptiles are more complex than those of amphibians. The walls of the lung cavity have many folds, where blood vessels branch repeatedly. This increases the surface of their contact with air, enhancing gas exchange.

Circulatory system. The heart is three-chambered, with an incomplete septum in the ventricle. Three large vessels emerge from it: the left and right aortic arches and the pulmonary artery (Fig. 145). The two arches of the aorta, bypassing the heart, merge into one common vessel - the dorsal aorta.

Rice. 145. Diagram of the structure of the circulatory system of a lizard: 1 - heart; 2 - carotid artery; 3 - left and right aortic arches; 4 - pulmonary artery; 5 - jugular (carries blood from the head) vein; 6 - intestinal vein; 7 - pulmonary vein; 8 - capillary network of internal organs

Mixed blood flows through the body, like amphibians, so reptiles have an unstable body temperature, which depends on the ambient temperature.

The pulmonary artery divides into two branches, which carry venous blood to the left and right lungs. Here it is saturated with oxygen. The pulmonary veins carry arterial blood into the left atrium. In the ventricle, the blood is partially mixed, the richest in oxygen goes to the head, mixed - to all organs of the body, saturated with carbon dioxide - to the lungs.

Nervous system. In reptiles, compared to amphibians, all parts of the brain are complicated and enlarged (Fig. 146). This is due to the more complex and diverse behavior of reptiles. They form conditioned reflexes faster than fish and amphibians. The forebrain and cerebellum are especially enlarged; the medulla oblongata forms a bend characteristic of all higher vertebrates. In addition to vision and smell, reptiles have a well-developed sense of touch.

Rice. 146. Diagram of the structure of the lizard brain: 1 - forebrain; 2 - diencephalon; 3 - midbrain; 4 - cerebellum; 5 - medulla oblongata

Excretory system. The excretory system of reptiles is the same as that of all terrestrial vertebrates. In the excretory organs - the kidneys - the mechanism for returning water to the body is strengthened. Therefore, the final product of metabolism in reptiles is not excreted in the form of liquid urine (as in amphibians), but in the form of uric acid in a pasty state into the cloaca and then out. Eliminating mushy uric acid from the body does not require as much fluid as liquid urine.

Reproductive organs. In reptiles, like other vertebrates, the reproductive organs of males are the testes, and the reproductive organs of females are the ovaries (Fig. 147). Fertilization in reptiles is internal. Seminal fluid enters the female's genital tract when the cloaca of the male and female come together. The embryo in the fertilized egg develops already when the egg moves along the oviduct and becomes covered with egg membranes. They provide the embryo with water and protect it from damage and shock.

Rice. 147. Diagram of the structure of the lizard oviduct: 1 - ovary; 2 - oviduct funnel; 3 - advancement of the fertilized egg along the oviduct; 4 - egg, covered with membranes, in the cloaca

Reptiles lay eggs on the ground or in specially prepared depressions (Fig. 148). Some reptiles protect their clutches (for example, crocodiles); others, having laid eggs, leave them (for example, turtles). Sometimes the babies develop in the mother's body. In these cases, ovoviviparity occurs. For example, in the viper and the viviparous lizard, the young hatch from the egg when it is laid.

Rice. 148. A turtle laying eggs (A), and the emergence of a young turtle from the egg (B)

Annual life cycle. Reptiles are widespread around the globe and are found in different climatic zones. However, being cold-blooded animals with an unstable body temperature, they need heat from the outside. Therefore, these animals are most numerous in the tropical and subtropical zones of the globe. In a seasonal climate, where warm summer gives way to cold autumn and winter, reptiles, with the onset of unfavorable conditions, go into shelters: holes, caves, under tree roots, in the basements of rural houses and forest huts. There the animals fall into torpor - hibernation. In the spring, when the air and soil surface warm up well, reptiles come to the surface and begin an active lifestyle.

Reptiles are well adapted to living on land: they breathe with lungs, they have internal fertilization, and the egg is covered with protective membranes that provide the developing embryo with water and nutrients. Body temperature depends on the environment. During unfavorable times of the year, reptiles spend time in shelters, falling into torpor; during favorable periods, they are active.

Exercises based on the material covered

1. What complications in the structure of the respiratory system can be noted in reptiles compared to amphibians?
2. Tell us about the structure of the circulatory system of reptiles. Why are they cold-blooded animals?
3. Compare the structure of the nervous system of reptiles and amphibians. How does the more complex behavior of reptiles affect the structure of their brains?
4. What behavioral features of reptiles contribute to successful reproduction?
5. Why are reptiles most common in tropical and subtropical zones of the globe?

Reptiles are the first terrestrial vertebrates; some species again switched to an aquatic lifestyle.

External structure

The eggs of reptiles are large, rich in yolk and protein, covered with a dense parchment-like shell, and develop on land or in the mother’s oviducts. There is no aquatic larva. A young animal born from an egg differs from adults only in size.

Dry skin is covered with horny scales and scutes.

1. Nostrils
2. Eyes
3. Head
4. Torso
5. Eardrum
6. Scales
7. Claws
8. Forelimb
9. Hind limb
10. Tail

Internal structure of a lizard

Digestive system

Mouth, oral cavity, pharynx, stomach, digestive glands, pancreas, liver, small and large intestines, cloaca - these are the parts of the digestive system of reptiles.

In the mouth, saliva moistens food, making it easier to move through the esophagus. In the stomach, under the influence of gastric juice, protein foods are digested in an acidic environment. The ducts of the gallbladder, liver and pancreas open into the intestine. Here food digestion is completed and nutrients are absorbed into the blood. Undigested food remains are expelled through the cloaca.

Excretory system

The excretory organs are the kidneys, ureters and bladder.

Skeleton

The skeleton is completely bony. The spine is divided into five sections: cervical, thoracic, lumbar, sacral and caudal. The head is mobile due to the elongation of the neck and the presence of two specialized cervical vertebrae.

1. Scull
2. Spatula
3. Bones of the forelimb
4. Spine
5. Ribs
6. Pelvic bones
7. Bones of the hind limb

Cervical region consists of several vertebrae, with the first two allowing the head to rotate in any direction. And this is extremely important for orientation using the senses located on the head.

Thoracic region It secures the shoulder girdle through the chest and provides support for the forelimbs. Lumbar provides bending of the body that helps movement. Powerful sacral region It already consists of two vertebrae and the belt of the hind limbs is numb. Long tail the section provides balancing movements of the tail.

Since the oral cavity no longer participates in gas exchange, the jaws have become elongated, more suitable for their main function - capturing food. Stronger jaw muscles attached to the new projections on the skull allowed for a significantly expanded diet.

Organ systems

Respiratory

Breathing is only pulmonary. The breathing mechanism is of the suction type (breathing occurs by changing the volume of the chest), more advanced than that of amphibians. Conducting airways (larynx, trachea, bronchi) are developed. The inner walls and septa of the lungs have a cellular structure.

Blood

The heart is three-chambered, consisting of two atria and one ventricle. The ventricle has an incomplete septum. The systemic and pulmonary circulations are not completely separated, but the venous and arterial flows are more clearly separated, so the body of reptiles is supplied with more oxygenated blood.

The right atrium receives venous blood from all organs of the body, and the left atrium receives arterial blood from the lungs. When the ventricle contracts, its incomplete septum reaches the dorsal wall and separates the right and left halves. From the left half of the ventricle, arterial blood enters the vessels of the brain and the anterior part of the body; from the right half, venous blood goes to the pulmonary artery and further to the lungs. The trunk region receives mixed blood from both halves of the ventricle.

Nervous

The brain is more developed, especially the forebrain hemispheres (responsible for complex instincts), the optic lobes and the cerebellum (coordinator of movements).

Sense organs

Sense organs are more complex. The reptile's eyes distinguish between moving and stationary objects. The lens in the eyes can not only move, but also change its curvature. Lizards have movable eyelids. In the olfactory organs, part of the nasopharyngeal passage is divided into olfactory and respiratory sections.

The internal nostrils open closer to the throat, so reptiles can breathe freely when they have food in their mouths.

Fertilization

Life appeared in water. Metabolic reactions occur in aqueous solutions. Water makes up the largest part of any organism. Individual development of the body requires significant amounts of water. Finally, without water, sperm movement and egg fertilization are impossible. That is why even in amphibians, fertilization and development are strongly associated with the aquatic environment. Overcoming this connection by reptiles is a major breakthrough in evolution.

The transition to reproduction on land was possible only for animals capable of internal fertilization.

Male reptiles have a special organ in the form of a permanent or temporary protrusion, with the help of which seminal fluid from the testes is introduced into the female’s genital tract. This helps protect the sperm from drying out and allows them to move. To meet them, eggs formed in the ovaries descend through the oviduct. There, in the oviduct, the fusion of gametes occurs.

Development

A fertilized egg is a large spherical yolk with a spot of an embryo on it. Descending along the oviduct, the egg is surrounded by egg membranes, of which in reptiles the parchment membrane is the most pronounced. It replaces the mucous membrane of amphibian eggs and protects the egg from external influences on land.

In May - June, the female lays 6-16 eggs in a shallow hole or burrow. The eggs are covered with a soft, fibrous, leathery shell that protects them from drying out. Eggs have a lot of yolk, the white shell is poorly developed. Already at the beginning of the development of the embryo, an extraembryonic bubble is formed from its tissues, which gradually surrounds the embryo on all sides. The embryo, along with the yolk, is suspended inside the egg. The outer shell of the bladder - serosa - creates antimicrobial protection. The inner membrane - the amnion - limits the amniotic cavity, which is filled with fluid. It replaces the embryo with a pool of water: it protects against tremors.

Cut off from the outside world, the fetus could suffocate and be poisoned by its own secretions. These problems are solved by another bladder - the allantois, which is formed from the hindgut and grows into the first bladder. Allantois accepts and isolates all the products of the embryo's excretion, and returns water back. Blood vessels develop in the walls of the allantois, which approach the surface of the egg and ensure the exchange of gases through the membranes of the egg. Thus, the allantois simultaneously plays the role of an embryonic organ of excretion and respiration. All development takes place over 50-60 days, after which the young lizard hatches. The young cub is ready to live on land. It differs from an adult only in its smaller size and underdeveloped reproductive system.

Regeneration

Various birds, small animals and snakes feed on lizards. If the pursuer manages to grab the lizard by the tail, then part of it is thrown away, which saves it from death.

Throwing the tail is a reflex response to pain; it is carried out by breaking one of the vertebrae in the middle. The muscles around the wound contract and there is no bleeding. Later, the tail grows back - regenerates.