The forelimb, when walking and standing, performs a supporting function, as well as a gripping function. It is divided into a shoulder girdle connected to the body and a free limb.

Shoulder girdle

In carnivores that have to run and jump a lot, the skeleton of the shoulder girdle is reduced. Only the shoulder blade is fully developed. The clavicle is an isolated bone, not connected through joints to the shoulder girdle.

Shoulder blade, scapula– round-triangular bone plate. on her outer surface there is a spine of the scapula, dividing it into the prespinous fossa and an almost equal post-spinous fossa. The scapular spine ends with a well-defined acromion (humeral process), reaching the plane of the glenoid cavity. The acromion has a palpable uncinate process, from which the cat's suprachonoid process arises. The anterior angle of the base of the scapula is rounded. The scapular cartilage is small. On the medial or costal surface, which is adjacent to the anterior chest wall and in a cat to the base of the neck, there is a subscapular fossa and a serrated surface. The latter extends almost to the dorsal margin, along which the narrow scapular cartilage runs. The cranial margin is convex. At its ventral end there is a notch of the scapula, deeper in a cat, for the passage of blood vessels and nerves. The cranial edge passes into the neck of the scapula. The caudal edge runs perpendicular to the neck of the scapula and in the dog has an articular tubercle at the lower end behind. The glenoid cavity is oval, equipped with an oval articular surface, the higher edge of which in cats and dachshunds bears a craniomedial notch of the glenoid cavity. The supraglenoid tubercle rises in front of the glenoid cavity. On the medial surface there is a coracoid (coracoid) process, in the dog in the form of a barely noticeable protrusion, in the cat in the form of a noticeable cylindrical process.

Clavicle, clavicula, is a vestigial bone. It lies in the tendon strip in the brachiocephalic muscle. In a dog, the collarbone is a bone plate 6-12 mm long and 4 mm wide; often it is completely absent. In a cat, the collarbone is always preserved and looks like a curved stick 2-30 mm long. Its ends are thickened and can be palpated.

Free limb

Humerus, humerus, in dogs it can have different lengths depending on the breed. In dachshunds and other chondrodystrophoid breeds, the humerus is shorter and wider, curved and slightly twisted around its axis. A cat's humerus is thin. Above the distal trochlea there is (excluding Foxes and Dachshunds) a supratrochlear foramen leading into the antecubital fossa. Due to the weak development of the tubercles, the intertubercular groove is flat; the lateral tubercle does not project above the head.

Bones of the forearm. The skeleton of the forearm consists of the radius and ulna bones, movably connected to each other. In a cat, unlike a dog, the degree of mobility of the bones relative to each other is much greater. In a cat, both bones are approximately the same size; in a dog (with the exception of dachshunds), the distal part of the ulna gradually becomes thinner. The two bones are connected, among other things, by the interosseous membrane of the forearm, which covers the interosseous space of the forearm.

Both bones of the forearm - the radius and ulna - are connected movably. The radius is long, thin, and dorsally curved. Head fossa radius oval; on the mediovolar surface of the head a transverse, narrow, long facet for the ulna is visible. A small facet for the same bone is also present on the distal epiphysis of the radius on its lateral surface. The articular surface for the carpal bones is a transverse oval fossa.

Front paw bones

Carpal bones. There are only three bones in the proximal row, since the radius and intermediate carpal bones have fused into one - the intermediate radius - with a convex proximal surface and four facets on the distal surface. The ulnar carpal bone is similar to the previous one, but smaller in size and with only three distal facets. The accessory bone is cylindrical in shape. There are four bones in the distal row: I bone of the wrist is trapezoidal, flat, II bone of the wrist is a triangular plate with a convex surface, III is strongly compressed laterally, IY is triangular in shape, the proximal convex surface with a ridge.

Metacarpal bones I-Y are long, with typical distal blocks. Of the five bones, III and IY are the longest; in cross section they are tetrahedral. The lateral II and Y bones are shorter, triangular in cross section: the I bone is the shortest. The proximal epiphyses of the bones form convex and laterally compressed articular surfaces. The pulleys on the distal epiphyses have a ridge only on their polar surface, while the anterior surface of the pulley is smooth, which allows lateral movements of the fingers when they are extended. When bending, lateral movements of the fingers are excluded.

Finger bones. The first and second phalanges are thin, long, cylindrical, symmetrical. On the claw surface, a proximal, widened end and a claw hook are distinguished, separated from each other by a claw groove. At the proximal end there is an articular surface for the second phalanx and posteriorly a flexor tubercle for the attachment of the deep flexor of the digitorum.

Sesamoid bones The first phalanges are strongly compressed laterally. The sesamoid bone of the third phalanx is absent.

Target:

Study the structure and species features bones forming the shoulder girdle: scapula.

To study the structure and specific features of the bones of the free part of the limb: the humerus.

Educational visual aids

1. Tables - bones of the peripheral skeleton of domestic animals and birds.

2. Skeletons of domestic animals and birds.

3. Shoulder blade and humerus of a dog, pig, cattle, horse.

Teaching Methodology

1. There are four sets of study materials on the students’ tables.

2. On the teacher’s table there are demonstration preparations and a set of training preparations.

3. Tables are posted on the board and a record of Latin terms is made.

4. The teacher explains the content of the lesson (35 min).

5. Independent work of students (30 min).

6. Checking the quality of assimilation of the studied material (20 min).

7. Answers to questions and homework (5 min).

1. Familiarize yourself with the general structure of the bones of the thoracic limb.

2. Study the structure of the scapula and humerus, as well as species characteristics in various species of domestic animals and birds.

Shoulder blade – scapula

lamellar, triangular bone

Costal surface – faсies costalis.

1. Serrated roughness – tuberositas serrata.

2. Subscapular fossa – fossa subscapularis.

Lateral surface – faсies lateralis.

1. Spine of the scapula – spinae scapulae.

2. Tubercle of the spine of the scapula – tuber spinae scapulae.

3. Acromion - acromion.

4. Prespinatus fossa – fossa supraspinata.

5. Infraspinous fossa – fossa infraspinata.

Edges: cranial, dorsal, caudal - margo cranialis, dorsalis, caudalis.

Angles: cranial, caudal, ventral – angulus cranialis, caudalis, ventralis.

Cartilage of the scapula – cartilago scapulae.

Scapula notch – incisura scapulae.

The neck of the scapula is collum scapulae.

The glenoid cavity is cavitas glenoidalis.

1. Supraarticular tubercle – tuberculum supraglenoidale.

2. Caracoid process – processus carаcoideus.

Species features:

Dog. The acromion hangs over the neck of the scapula and has uncinate process - hamatus, the cartilage of the scapula is poorly developed, the cranial angle of the scapula is rounded.

Pig. The tubercle of the spine of the scapula is strongly developed and hangs over the infraspinous fossa, the acromion is absent, and the scapular cartilage is small.

Cattle. The infraspinous fossa is three times wider than the prespinous fossa, the acromion reaches the neck of the scapula, the cartilage is small.

Horse. The tubercle of the spine and the caracoid process are well defined, the acromion is absent, the glenoid cavity has a notch, the scapular cartilage is highly developed, and the prespinatus fossa is narrow.

Humerus – os humerus

long, tubular bone

I. Proximal epiphysis– epiphisis proximalis.

1. Head of the humerus – caput humeri.

2. Neck of the humerus – collum humeri.

3. Greater tubercle – tuberculum majus.

The ridge of the greater tubercle is crista tuberculi majus.

The surface for the infraspinatus muscle is faсies musculi infraspinati.

Small round roughness – tuberositas teres minor.

The line of the three heads of the muscle is lineia musculi tricipitis.

4. Lesser tubercle – tuberculum minor.

5. Intertubercular groove – sulcus intertubercularis.

II. The body of the humerus is corpus humeri.

1. Surfaces: cranial, caudal, lateral, medial – faсies cranialis, caudalis, lateralis, medialis.

2. Large round roughness – tuberositas teres major.

3. Deltoid roughness – tuberositas deltoidea.

4. The crest of the humerus is crista humeri.

III. Distal epiphysis – epiphysis distalis.

1. Block of the humerus – trochlea humeri.

2. Radial fossa – fossa radialis.

4. Lateral and medial condyle – condylus lateralis, medialis.

5. Lateral and medial epicondyle – epicondylus lateralis, medialis.

Species features:

Dog. The bone is long, thin, there is supratrochlear foramen– foramen supratrochleare, greater tubercle does not protrude above the head.

Pig. The bone is short, part of the greater tubercle hangs over the intertubercular groove.

Cattle. The bone is short, the greater tubercle is extended proximally, part of it hangs over the intertubercular groove.

Horse. Available intermediate tubercle– tuberculum intermedium, two intertubercular grooves, the crest of the greater tuberosity and the deltoid roughness are large, there are synovial fossa - fossa synovialis.

Questions to reinforce learned material

1. What parts is the thoracic limb divided into?

2. Name the components of the lateral and medial surfaces of the scapula.

3. By what signs can you determine whether you have a right or left shoulder blade?

4. Name the animals that have an acromion of the scapula.

5. Name the specific features of the bones of the shoulder girdle of a dog, pig, cattle, horse.

6. What is located on the epiphyses and diaphysis of the humerus.

7. How to distinguish the right from the left humerus.

8. Name the specific features of the humerus of a dog, pig, cattle, horse.

Literature

Akaevsky A.I. “Anatomy of Domestic Animals” M. 1975. pp. 82-85.

Klimov A.F. "Anatomy of Domestic Animals", 2003. pp. 176-179.

Khrustaleva I.V., Mikhailov N.V. and others. “Anatomy of Domestic Animals” M. Kolos. 1994. pp. 128-154.

Popesco P. “Atlas of topographic anatomy of agriculture. animals." "Bratislava". 1961 T. 3.

Yudichev Yu.F. "Comparative Anatomy of Domestic Animals". Volume 1. Orenburg-Omsk. 1997. pp. 128-132.

Yudichev Yu.F., Efimov S.I. “Anatomy of Domestic Animals” Omsk. 2003. pp. 122-126.

Appendix, Fig. 22 - 23.

ANATOMY OF DOMESTIC ANIMALS

BODY PLANES AND TERMS TO DEnote ORGAN LOCATION

To determine the location of organs and parts, the animal’s body is dissected by three imaginary mutually perpendicular planes - sagittal, segmental and frontal (Fig. 1).

Median sagittal(median) plane is carried out vertically along the middle of the animal’s body from the mouth to the tip of the tail and dissecting it into two symmetrical halves. The direction in the animal's body towards the median plane is called medial, and from her - lateral(lateralis - lateral).

Fig.1. Planes and directions in the animal body

Planes:

I– segmental;

II - sagittal;

III– frontal.

Directions:

1 – cranial;

2 – caudal;

3 – dorsal;

4 – ventral;

5 – medial;

6 – lateral;

7 – rostral (oral);

8 – aboral;

9 – proximal;

10 – distal;

11 – dorsal

(back, back);

12 – palmar;

13 - plantar.

Segmental the plane is drawn vertically across the animal’s body. The direction from it towards the head is called cranial(cranium - skull), towards the tail – caudal(cauda - tail). On the head, where everything is cranial, the direction towards the nose is distinguished - nasal or proboscis - rostral and its opposite - caudal.

Frontal the plane (frons - forehead) is drawn horizontally along the animal’s body (with a horizontally elongated head), i.e. parallel to the forehead. The direction in this plane towards the back is called dorsal(dorsum - back), to the stomach – ventral(venter - belly).

To determine the position of parts of the limbs, there are terms proximal(proximus - closest) – closer position to the axial part of the body and distal(distalus - remote) - a more distant position from the axial part of the body. To designate the anterior surface of the limbs, the terms cranial or dorsal(for the paw), and for the back surface - caudal, and palmar or volar(palma, vola - palm) – for the hand and plantar(planta - foot) – for the foot.

DIVISIONS AND AREAS OF ANIMAL BODY AND THEIR BONE BASIS

The body of animals is divided into the axial part and limbs. Starting with amphibians, in animals the axial part of the body is divided into the head, neck, torso and tail. The neck, body and tail make up body trunk. Each part of the body is divided into sections and regions (Fig. 2). In most cases, they are based on the bones of the skeleton, which have the same names as the areas.

Rice. 2 Cattle body areas

1 - frontal; 2 - occipital; 3 - parietal; 4 - temporal; 5 - parotid; 6 - auricle; 7 - nasal; 8 - areas of the upper and lower lips; 9 - chin; 10 - buccal; 11 - intermaxillary; 12 - infraorbital; 13 - zygomatic; 14 - eye area; 15 - large masseter muscle; 16 - upper cervical; 17 – lateral cervical; 18 - lower cervical; 19 - withers; 20 - backs; 21 - costal; 22 - presternal; 23 - sternal: 24 - lumbar: 25 - hypochondrium; 26 - xiphoid cartilage; 27 - paralumbar (hungry) fossa; 28 - lateral area; 29 - inguinal; 30 - umbilical; 31 - pubic; 32 - maklok; 33 – sacral; 34 - gluteal; 35 - root of the tail; 36 - ischial region; 37 - shoulder blade; 38 - shoulder; 39 - forearm; 40 - brush; 41 - wrist; 42 - metacarpus; 43 - fingers; 44 - hip; 45 - shin; 46 - foot; 47 - tarsus; 48 - metatarsus

Head(Latin caput, Greek cephale) is divided into the skull (cerebral region) and the face (facial region). The skull (cranium) is represented by the regions: occipital (back of the head), parietal (crown), frontal (forehead) with the horn region in cattle, temporal (temple) and parotid (ear) with the auricle region. On the face (facies) the following areas are distinguished: orbital (eyes) with the areas of the upper and lower eyelids, infraorbital, zygomatic with the area of ​​the large masticatory muscle (in a horse - ganache), premaxillary, chin, nasal (nose) with the area of ​​the nostrils, oral (mouth) , which includes the areas of the upper and lower lips and cheeks. Above the upper lip (in the area of ​​the nostrils) there is a nasal mirror; in large ruminants it extends to the area upper lip and becomes nasolabial.

Neck

The neck (cervix, collum) extends from the occipital region to the scapula and is divided into areas: the upper cervical, lying above the bodies of the cervical vertebrae; lateral cervical (brachiocephalic muscle area), running along the vertebral bodies; the lower cervical, along which the jugular groove stretches, as well as the laryngeal and tracheal (on its ventral side). Ungulates have relatively long necks due to the need to feed on pasture. Fast-gaited horses have the longest necks. The shortest is that of a pig.

Torso

The trunk (truncus) consists of the thoracic, abdominal and pelvic sections.

Thoracic region includes the areas of the withers, back, lateral costal, presternal and sternal. It is durable and flexible. In the caudal direction, strength decreases, and mobility increases due to the peculiarities of their connection. The bone base of the withers and back are the thoracic vertebrae. In the area of ​​the withers they have the highest spinous processes. The higher and longer the withers, the larger the area of ​​attachment of the muscles of the spine and the girdle of the thoracic limb, the wider and more elastic the movements. There is an inverse relationship between the length of the withers and the back. The horse has the longest withers and the shortest back; the pig has the opposite.

Abdominal includes the lower back (lumbus), stomach (abdomen), or belly (venter), therefore it is also called the lumbo-abdominal region. The lower back is the continuation of the back to the sacral region. Its basis is the lumbar vertebrae. The abdomen has soft walls and is divided into a number of areas: the right and left hypochondrium, the xiphoid cartilage; paired lateral (iliac) with a hungry fossa, adjacent from below to the lower back, in front to the last rib, and from behind it passes into the groin area; umbilical, lying in the lower abdomen behind the region of the xiphoid cartilage and in front of the pubic region. On the ventral surface of the areas of the xiphoid cartilage, umbilical and pubic cartilage in females there are mammary glands. The horse has the shortest loin and less extensive abdominal region. Pig and cattle have a longer loin. The abdominal region is the most voluminous in ruminants.

Pelvic region(pelvis) is divided into areas: sacral, gluteal, including macular, ischial and perineal with the adjacent scrotal region. The tail (cauda) is divided into root, body and tip. The areas of the sacrum, two buttocks and the root of the tail form the croup in a horse.

Limbs(membra) are divided into thoracic (anterior) and pelvic (rear). They consist of belts that connect to the stem part of the body, and free limbs. The free limbs are divided into the main supporting pillar and the paw. The thoracic limb consists of the shoulder girdle, upper arm, forearm and hand.

Regions shoulder girdle And shoulder adjacent to the lateral thoracic region. The bony basis of the shoulder girdle in ungulates is the scapula, which is why it is often called the scapula region. Shoulder(brachium) is located below the shoulder girdle and has the shape of a triangle. The bone base is the humerus. Forearm(antebrachium) is located outside the skin trunk sac. Its bone base is the radius and ulna. Brush(manus) consists of the wrist (carpus), metacarpus (metacarpus) and fingers (digiti). In animals of different species there are from 1 to 5. Each finger (except the first) consists of three phalanges: proximal, middle and distal (which in ungulates are called fetlock, respectively, in horses - pastern), coronary and hoof (in horses - ungulate) .

The pelvic limb consists of the pelvic girdle, thigh, lower leg and foot.

Region pelvic girdle(pelvis) is part of the axial part of the body as the gluteal region. The bone base is the pelvic or innominate bones. Region hips(femur) located under the pelvis. The bone base is the femur. Region shins(crus) is located outside the skin trunk sac. The bone base is the tibia and fibula. Foot(pes) consists of the tarsus (tarsus), metatarsus (metatarsus) and fingers (digiti). Their number, structure and names in ungulates are the same as on the hand.

SOMATIC SYSTEMS

The skin, skeletal muscles and skeleton, forming the body itself - the soma of the animal - are united into a group of somatic systems of the body.

The movement apparatus is formed by two systems: bone and muscle. The bones combined into the skeleton represent a passive part of the movement apparatus, being levers on which the muscles attached to them act. Muscles act only on bones that are movably connected by ligaments. The muscular system is the active part of the movement apparatus. It ensures the movement of the body, its movement in space, search, capture and chewing of food, attack and defense, breathing, eye movements, ears, etc. It accounts for 40 to 60% of the body's mass. It determines the shape of the animal’s body (exterior), proportions, determining the typical features of the constitution, which is of great practical importance in animal science, since endurance, adaptability, fattening ability, precocity, sexual activity, vitality are associated with the features of the exterior and the type of constitution, and other qualities of animals.

SKELETON, CONNECTION OF SKELETAL BONES (OSTEOLOGY)

General characteristics and significance of the skeleton.

The skeleton (Greek skeleton - withered, mummy) is formed by bones and cartilage, interconnected by connective, cartilaginous or bone tissue. The mammalian skeleton is called internal because it is located under the skin and covered with a layer of muscles. It is the solid foundation of the body and serves as a case for the brain, spinal cord and bone marrow, for the heart, lungs and other organs. The elasticity and spring properties of the skeleton ensure smooth movements and protect soft organs from shocks and shocks. The skeleton is involved in mineral metabolism. It contains large reserves of calcium salts, phosphorus and other substances. The skeleton is the most accurate indicator of the degree of development and age of an animal. Many palpable bones are permanent landmarks when taking zootechnical measurements of an animal.

SKELETAL DIVISION

The skeleton is divided into axial and limb skeleton (peripheral) (Fig. 3).

The axial skeleton includes the skeleton of the head, neck, trunk and tail. The skeleton of the torso consists of the skeleton of the chest, lower back and sacrum. The peripheral skeleton is formed by the bones of the girdles and free limbs. Number of bones in animals different types, breeds and even individuals are not the same. The skeletal mass of an adult animal ranges from 6% (pig) to 12-15% (horse, bull). In newborn calves – up to 20%, and in piglets – up to 30%. from body weight. In newborns, the peripheral skeleton is more developed. It accounts for 60-65% of the mass of the entire skeleton, and the axial part accounts for 35-40% . After birth, it grows more actively, especially in milk period, axial skeleton and in an 8-10-month-old calf, the relationships of these skeletal sections level out, and then the axial skeleton begins to predominate: at 18 months in cattle it is 53-55%. In a pig, the mass of the axial and peripheral skeleton is approximately the same.

Fig.3 Skeleton of a cow (A), pig (B),

horses (B)

Axial skeleton: 1- bones brain section(skull): 3- bones of the facial section (face); A- cervical vertebrae; 4 - thoracic vertebrae; 5 - ribs; 6 - sternum; 7 - lumbar vertebrae: 8 - sacral bone: 9 - host vertebrae (3,4,7,8,9 - spine). Skeleton of limbs; 10 - blade; 11 - humerus; 12 - bones of the forearm (radius and ulna); 13 - carpal bones; 14 - metacarpus bones; 15 - finger bones (IS-15 - hand bones); 16 - pelvic bone; P - femur: IS - patella; IS - tibia bones (tibia and fibula); 30 - tarsal bones: 31 - metatarsal bones; 32 - finger bones (20-22 - foot bones).

Shape and structure of bones

Bone (lat. os) is an organ of the skeletal system. Like any organ, it has a certain shape and consists of several types of tissue. The shape of the bones is determined by the characteristics of its functioning and position in the skeleton. There are long, short, flat and mixed bones.

Long bones are tubular (many limb bones) and arched (ribs). The length of both is greater than the width and thickness. The long tubular bones resemble a cylinder in shape with thickened ends. The middle, narrower part of the bone is called the body - diaphysis(Greek diaphysis), extended ends – epiphyses(epiphysis). These bones play a major role in statics and dynamics, in hematopoietic function (contain red bone marrow).

Short Bones usually small in size, their height, width and thickness are similar in size. They often perform a spring function.

Flat bones have a large surface (width and length) with a small thickness (height). Usually they serve as the walls of cavities, protecting the organs placed in them (the cranium) or this extensive field for muscle attachment (scapula).

Mixed dice have a complex shape. These bones are usually unpaired and are located along the axis of the body. (occipital, sphenoid bones, vertebrae). Paired mixed bones are asymmetrical, such as the temporal bone.

Bone structure

The main tissue that forms bone is lamellar bone. The bone also includes reticular, loose and dense connective tissue, hyaline cartilage, blood and vascular endothelium, and nerve elements.

Outside the bone is dressed periosteum, or periostomy, except location articular cartilage. The outer layer of the periosteum is fibrous, formed by connective tissue with a large number of collagen fibers; determines its strength. The inner layer contains undifferentiated cells that can transform into osteoblasts and are the source of bone growth. Vessels and nerves penetrate the bone through the periosteum. The periosteum largely determines the viability of the bone. The bone, cleared of periosteum, dies.

Under the periosteum lies a layer of bone formed by densely packed bone plates. This compact substance of bone. In tubular bones, several zones are distinguished. The zone adjacent to the periosteum external general plates thickness 100-200 microns. It gives the bone greater hardness. This is followed by the widest and most structurally important zone osteons. The thicker the layer of osteons, the better the spring properties of the bone. In this layer between the osteons lie insert plates – remnants of old destroyed osteons. In ungulates it often contains circular-parallel structures resistant to bending resistance. It is no coincidence that they are widespread in the long tubular bones of ungulates, which experience great pressure. The thickness of the inner layer of the compact substance is 200-300 microns, it is formed internal general plates or passes into the spongy bone.

Spongy substance represented by bone plates that are not tightly adjacent to each other, but form a network of bone bars(trabeculae), in the cells of which the red bone marrow is located. The spongy substance is especially developed in the epiphyses. Its crossbars are not arranged randomly, but strictly follow the lines of the acting forces (compression and tension).

In the middle of the diaphysis of the tubular bone there is bone cavity. It was formed as a result of the resorption of bone tissue by osteoclasts during bone development and is filled yellow(fat) bone marrow.

The bone is rich in vessels that form a network in its periosteum, penetrate the entire thickness of the compact substance, being in the center of each osteon, and branch in the bone marrow. In addition to osteon vessels, bones contain the so-called. nutrient vessels(Volkmann's), perforating the bone perpendicular to its length. Concentric bone plates do not form around them. There are especially many such vessels near the epiphyses. Nerves enter the bone from the periosteum through the same openings as the vessels. The surface of the bone is covered with hyaline cartilage without perichondrium. Its thickness is 1-6 mm and is directly proportional to the load on the joint.

The structure of short, complex and flat bones is the same as tubular ones, with the only difference being that they usually do not have bone cavities. The exception is some flat bones of the head, in which between the plates of the compact substance there are vast spaces filled with air - sinuses or sinuses.

SKELETAL PHYLOGENESIS

The development of the support system in animal phylogeny followed two paths: the formation of the external and internal skeleton. The exoskeleton is formed in the integument of the body (arthropods). The internal skeleton develops under the skin and is usually covered by muscles. We can talk about the development of the internal skeleton since the appearance of chordates. In primitive chordates (lancelet) - chord is a support system. As the organization of animals becomes more complex, the connective tissue skeleton is replaced by cartilaginous and then bone.

Phylogeny of the stem skeleton

In the phylogeny of vertebrates, vertebrae appear earlier than other elements. As the organization becomes more complex, activity and variety of movements increase around the notochord, not only the arches, but also the vertebral bodies develop. In cartilaginous fish, the skeleton is formed by cartilage, sometimes calcified. In addition to the upper arches, they develop lower arches under the chord. The ends of the upper arches of each segment, merging, form the spinous process. Vertebral bodies appear . The chord loses its significance as a supporting rod. In bony fish, the cartilaginous skeleton is replaced by bone. Articular processes appear, with which the vertebrae articulate with each other, which ensures the strength of the skeleton while maintaining its mobility. The axial skeleton is divided into the head, trunk with ribs covering the body cavity with organs, and a highly developed caudal section - the locomotor section.

The transition to a terrestrial lifestyle leads to the development of some parts of the skeleton and reduction of others. The skeleton of the body is differentiated into the cervical, thoracic (dorsal), lumbar and sacral sections, the skeleton of the tail is partially reduced, since the main load when moving on the ground falls on the limbs. In the thoracic region, in close connection with the ribs, the sternum develops and forms rib cage. In amphibians, the cervical and sacral spines have only one vertebra; the lumbar spine is absent. The ribs are very short, in many they are fused with the transverse processes of the vertebrae. In reptiles, the cervical region lengthens to eight vertebrae and acquires greater mobility. In the thoracic region, 1-5 pairs of ribs are connected to the sternum - the rib cage is formed. Lumbar long, has ribs, the size of which decreases in the caudal direction. The sacral section is formed by two vertebrae, the caudal section is long and well developed.

In mammals, regardless of lifestyle, the number of cervical vertebrae is constant (7). The number of vertebrae in other sections is also relatively constant: 12-19 thoracic, 5-7 lumbar, 3-9 sacral. The number of caudal vertebrae ranges from 3 to 46. The vertebrae, with the exception of the first two, are connected by cartilaginous discs (menisci), ligaments and articular processes.

The surfaces of the cervical vertebral bodies often have a convex-concave shape - opisthocoelous. In other parts the vertebrae are usually flat - Platycoelous. The ribs are preserved only in the thoracic region. In the lower back they are reduced and fuse with the transverse processes of the vertebrae. IN sacral region the vertebrae also fuse, forming sacrum. The caudal region is lightened, its vertebrae are greatly reduced.

Phylogeny of the head skeleton

The skeleton of the head end of the body develops around the neural tube - the axial (cerebral) skeleton of the head and around the head intestine - visceral. The axial skeleton of the head is represented by cartilaginous plates surrounding the neural tube from below and from the sides; the roof of the skull is membranous. The visceral skeleton of the head consists of cartilaginous gill arches associated with the respiratory and digestive apparatus; there are no jaws. The development of the head skeleton proceeded by combining the cerebral and visceral skeletons and complicating their structure in connection with the development of the brain and sensory organs (smell, vision, hearing). The brain skull of cartilaginous fish is a solid cartilaginous box surrounding the brain. The visceral skeleton is formed by cartilaginous gill arches. The skull of bony fishes has a complex structure. The primary bones form the occipital region, part of the base of the skull, the olfactory and auditory capsules, and the wall of the orbit. The integumentary bones cover the primary cranium from above, below and from the sides. The visceral skeleton is very complex system levers involved in grasping, swallowing and breathing movements. The visceral skeleton articulates with the cranium using the pendant (hyomandibulare), resulting in the formation of a single skeleton of the head.

With access to land, with a sharp change in the habitat and lifestyle of animals, significant changes occur in the skeleton of the head: the skull is movably attached to the cervical region; the number of skull bones decreases due to their fusion; its strength increases. A change in the type of breathing (from gill to pulmonary) leads to a reduction of the gill apparatus and the transformation of its elements into the hyoid and auditory bones. The jaw apparatus fuses with the base of the skull. In the series of terrestrial animals, a gradual increase in complexity can be observed. There is a lot of cartilage in the skull of amphibians, auditory bone one. The mammalian skull is characterized by a decrease in the number of bones due to their fusion (for example, the occipital bone is formed by the fusion of 4, and the petrous - 5 bones), the erasing of the boundaries between the primary and integumentary (secondary) bones, the powerful development of the olfactory region and a complex sound-conducting apparatus, in large sizes of the skull, etc.

Phylogeny of the limb skeleton

The hypothesis about the origin of the limbs of land animals on the basis of paired fins of fish is now widely accepted. Paired fins in the chordate phylum first appeared in fish . The bony basis of paired fish fins is a system of cartilaginous and bone elements. The pelvic girdle in fish is less developed. With access to land, on the basis of paired fins, the skeleton of the limbs develops, divided into sections typical of a five-fingered limb . The limb girdles consist of 3 pairs of bones and are strengthened by connections with the axial skeleton: the shoulder girdle with the sternum, the pelvic girdle with the sacrum. The shoulder girdle consists of the coracoid, scapula and clavicle, the pelvic girdle - of the ilium, pubis and ischium. The skeleton of the free limbs is divided into 3 sections: in the front limb there are bones of the shoulder, forearm and hand, in the hind limb there are bones of the thigh, lower leg and foot.

Further transformations are related to the nature of movement, its speed and maneuverability. In amphibians, the girdle of the thoracic limbs, attached to the sternum, does not have a rigid connection with the axial skeleton. In the girdle of the pelvic limbs, its ventral part is developed. In reptiles, the dorsal and ventral parts of the girdle skeleton are equally developed.

The shoulder girdle of mammals is reduced and consists of two or even one bone. In animals with developed abductor movements of the thoracic limb (for example, moles, bats, monkeys), the scapula and clavicle are developed, while in animals with monotonous movements (for example, ungulates), only the scapula is developed. The pelvic girdle of mammals is strengthened by the fact that the pubic and ischial bones are connected ventrally to the spinal bones. The skeleton of the free limbs of mammals is organized so that the body of the animal is raised above the ground. Adaptation to various types of movement (running, climbing, jumping, flying, swimming) led to a strong specialization of the limbs in different groups of mammals, which is expressed mainly in changes in the length and angle of inclination of individual parts of the limbs, the shape of the articular surfaces, fusion of bones and reduction of fingers .

Changes in the structure of the limbs in phylogeny due to increased specialization - adaptation to a certain type of movement - have been studied in more detail in the series of horses (). The supposed ancestor of the horse, combining the features of ungulates and predators, was the size of a fox and had five-fingered limbs with claws similar in shape to hooves. From various soft movements on loose ground with tall vegetation (forest) to wide, sweeping, fast movements across dry open spaces (steppe), the main supporting pillar of the limbs was lengthened due to the opening (increase) of the angles between its links. The paw rose, the animal switched from foot-to-digital walking. At the same time, a gradual reduction of non-functioning fingers was observed. During the transition from finger-to-phalango (hoof-) walking, the entire paw is included in the main supporting column, and the reduction of the fingers reaches a maximum. In the horse, only the third toe remains fully developed on the limb. In cattle, two fingers, III and IV, are developed.

Skeletal ontogeny

In the process of individual development of an individual, the skeleton goes through the same 3 stages of development and in the same sequence as in phylogenesis: connective tissue, cartilaginous and bone skeleton.

Chord as one of the first axial organs, it is formed in the embryonic period of intrauterine development as a result of differentiation of endoderm and mesoderm during the period of gastrulation. Soon segmented mesoderm forms around it - somites, the inner part of which is sclerotomes, adjacent to the notochord are skeletogenic rudiments.

Connective tissue stage. In the area of ​​sclerotomes, there is an active proliferation of cells that take on the appearance of mesenchymal cells, grow around the notochord and turn into its connective tissue sheath and myosepta - connective tissue cords. The connective tissue skeleton in mammals exists for a very short time, since in parallel with the process of overgrowth of the notochord in the membranous skeleton, mesenchymal cells multiply, especially around the myosepta, and differentiate into cartilaginous cells.

Cartilaginous stage. The differentiation of mesenchymal cells into cartilaginous cells begins in the cervical region. The first to be laid are the cartilaginous arches of the vertebrae, which are formed between the notochord and spinal cord, grow over the spinal cord from the side and above, forming its sheath. Connecting with each other in pairs above the spinal cord, the arches form the spinous process. At the same time, from the concentrations of mesenchymal cells multiplying in the notochord sheath, the cartilaginous bodies of the vertebrae develop, and in the myosepta - the rudiments of the ribs and sternum. The replacement of connective tissue with cartilage begins in pigs and sheep at the 5th week of embryonic development, in horses and cattle - at the 6th week of embryonic development. Then, in the same sequence as the formation of the cartilaginous skeleton, its ossification occurs.

There are no vessels in the cartilaginous anlage (model) of the bone. With the development of the circulatory system of the embryo, vessels form around and inside the perichondrium, as a result of which its cells begin to differentiate not into chondroblasts, but into osteoblasts, i.e. it becomes periosteum - periosteum. Osteoblasts produce intercellular substance and deposit it on top of the cartilage rudiment of the bone. Formed bone cuff. The bony cuff is constructed from coarse fibrous bone tissue. The process of formation and growth of the cuff around the cartilaginous rudiment is called ossification.

The bone cuff makes it difficult for the cartilage to feed and begins to deteriorate. The first foci of calcification and destruction of cartilage are found in the center (diaphysis) of the cartilaginous rudiment. Vessels along with undifferentiated cells penetrate into the focus of decaying cartilage from the periosteum. Here they multiply and turn into bone cells - a first outbreak(center) ossification. Each bone usually has several foci of ossification (in the vertebrae of ungulates there are 5-6 of them, in the ribs - 1-3).

In the focus of ossification, osteoclasts destroy calcified cartilage, forming gaps And tunnels, width 50-800 microns. Osteoblasts produce intercellular substance, which is deposited along the walls of gaps and tunnels. The mesenchyme, penetrating along with the capillaries, gives rise to the next generation of osteoblasts, which, depositing intercellular substance towards the walls of the tunnels, wall up the previous generations of osteoblasts - develop bone plates. Since lacunae and tunnels form a network, the bone tissue lining them follows their shape and generally resembles a sponge consisting of intertwined bone cords, bars or trabeculae From them is formed spongy bone. The formation of bone inside the cartilaginous rudiment at the site of destroyed cartilage is called endochondral(enchondral) ossification.

Some of the undifferentiated cells that penetrate along with the capillaries into the tunnels and lacunae turn into bone marrow cells, which fill the spaces between the bone trabeculae of the spongy substance.

The process of enchondral ossification, starting in the area of ​​the diaphysis, spreads to the ends of the rudiment - the epiphyses. At the same time, the bone cuff thickens and grows. Under such conditions, cartilage tissue can only grow in longitudinal direction. In this case, chondroblasts, when multiplying, line up one above the other in the form cell columns(coin columns).

The formation of cartilaginous models and their ossification occur quickly in those areas of the body where the need for support appears very early. Based on the timing of formation and the rate of differentiation of the bone skeleton, mammals can be divided into several groups. Ungulates belong to a group in which the formation and formation of ossification foci is almost completed at the time of birth, 90% of the bone is formed bone tissue. After birth, only the growth of these lesions continues. Newborns of such animals are active, they can immediately move independently, follow their mother and get food for themselves.

Primary foci of ossification during the prefetal period are noted in the skeleton of the body. In cattle, the ribs ossify first. Ossification of the vertebrae begins from the atlas and spreads caudally. The bodies ossify primarily at the middle thoracic vertebrae. In the second half of embryonic development, osteons are actively formed, layers are distinguished external and internal general plates. In postnatal ontogenesis, new layers of bone tissue grow until the animal’s growth is complete, as well as the restructuring of existing osteons.

The zone of cell columns is constantly growing on the side of the epiphyses due to the differentiation of cartilaginous cells from the perichondrium. On the part of the diaphysis, there is constant destruction of cartilage due to disruption of its nutrition and changes in tissue chemistry. As long as these processes balance each other, the bone grows in length. When the rate of enchondral ossification becomes greater than the rate of growth of metaepiphyseal cartilage, it becomes thinner and completely disappears. From this time on, the linear growth of the animal stops. In the axial skeleton, cartilage is preserved longest between the epiphyses and the vertebral body, especially in the sacrum.

In the enchondral bone, the growth of bone in width begins from the diaphysis and is expressed in the destruction of old and the formation of new osteons, in the formation of a bone cavity. In the perichondral bone, the restructuring consists of the fact that the coarse fibrous bone tissue of the cuff is replaced by lamellar bone tissue in the form of osteons, circularly parallel structures and general plates, which together make up compact substance of bone. During the restructuring process, intercalary plates are formed. In cattle and pigs, the axial skeleton begins to ossify at 3-4 years, and the process is completely completed at 5-7 years, in a horse - at 4-5 years, in sheep - at 3-4 years.

Skull development

The axial skull begins with 7-9 somites. Around the terminal portion of the notochord, the sclerotomes of these somites form a continuous membranous plate without traces of segmentation. It extends forward (prechordal) and covers the brain vesicles, auditory and olfactory capsules and optic cups from below and from the sides. The replacement of the connective tissue axial skull with cartilage begins near the anterior end of the notochord under the base of the brain. This is where the pair is laid perichordates(parochordalia) cartilage. Further in the oral direction two cartilaginous beams or trabeculae. Since they lie in front of the notochord, this section of the axial skull is called prechordal. Trabeculae and parachordalia, growing, merge together, forming main cartilaginous plate. In the oral part, along the main cartilaginous plate, a cartilaginous nasal septum is formed, on both sides of which the nasal turbinates develop. The cartilage is then replaced primary or primordial bones. The primary bones of the axial skull are the occipital, sphenoid, petrosal and ethmoid, forming the floor, anterior and posterior walls of the cranial cavity, as well as the nasal septum and conchae. The rest of the bones secondary, cutaneous, or integumentary, because they arise from the mesenchyme, bypassing the cartilaginous stage. These are the parietal, interparietal, frontal, temporal (scales), forming the roof and side walls of the cranial cavity.

Parallel to the development of the axial skull, the transformation of the visceral skeleton of the head occurs. Most of the rudiments of the visceral arches undergo complete reduction, and part of their material goes to the formation auditory ossicles, hyoid bone and laryngeal cartilage. The bulk of the bones of the visceral skeleton are secondary, integumentary. The axial and visceral skeleton of the mammalian head are so closely connected to each other that the bones of one are part of the other. Therefore, the skull of mammals is divided into brain section(the skull itself), which is the seat of the brain, and facial section(face), forming the walls of the nasal and oral cavity. During the fetal period, the shape of the skull is determined, characteristic of the species and breed. Fontanas - non-ossified areas - are covered with dense connective tissue or cartilage.

Limb development

The limbs of mammals are formed in the form of outgrowths of the cervicothoracic and lumbosacral somites. In cattle this occurs in the 3rd week. Their segmentation is not expressed. The anlage looks like accumulations of mesenchyme, which quickly increase in length, turning into lobe-shaped outgrowths. First, these outgrowths are divided into two units: the anlage of the belts and free limbs, not divided into sections and bones. Then connective tissue and cartilaginous bone anlages are differentiated from the mesenchyme thickenings. During the process of differentiation, the skeleton of the limbs goes through the same three stages as the stem skeleton, but with some lag. Ossification of the limbs in a fetal calf begins at 8-9 weeks and proceeds similarly to the stem skeleton. Many bone outgrowths - apophyses. have their own foci of ossification. During the process of ossification, a spongy and compact substance is formed in the tubular bones. Restructuring from the center of the bone spreads to its periphery. At the same time, in the area of ​​the diaphysis, due to the activity of osteoclasts, the spongy substance almost completely disappears, remaining only in the epiphyses. The bone cavity increases. The red bone marrow turns yellow in it.

Layers of compact substance become noticeable during the first months of life. The degree of its development depends on the type of animal. In ungulates, general plates and circular-parallel structures are well developed in it; in carnivores, osteons predominate. This is due to differences in the functional loads of the bones, especially the limbs. In ungulates they are adapted to rectilinear movement and retention of a massive body, in carnivores - to more light body and various movements.

In the extremities, foci of ossification appear in the bones of the girdles, then spreading in the distal direction. Final ossification (synostosis) primarily occurs in the distal links. Thus, in cattle, ossification of the distal parts of the limb (tarsus and metacarpus) is completed by 2-2.5 years, by 3-3.5 years all the bones of the free limb ossify, and the bones of the pelvic girdle - only by 7 years.

Age-related changes in the skeleton

Due to different timing of formation, growth rate and ossification of skeletal bones, changes in body proportions occur during ontogenesis. During embryonic development, bones grow at different rates. In ungulates, the axial skeleton grows more intensively in the first half, and the skeleton of the limbs in the second half. Thus, in 2-month-old fetal calves, the axial skeleton is 77%, the skeleton of the limbs is 23%, and by birth it is 39 and 61%. According to the data, from the time of cartilaginous anlage (1-month embryo) to birth, the skeleton of the pelvic limb with a belt in merino sheep increases 200 times, the thoracic limb - 181 times, the pelvis - 74 times, the spine - 30 times, the skull - 24 times. times. After birth, the increased growth of the peripheral skeleton is replaced by linear growth of the axial skeleton.

In postnatal ontogenesis, the skeleton grows at a lower rate than muscles and many internal organs, so its relative mass decreases by 2 times. During the process of bone growth and differentiation, their strength increases, which is associated with an increase in the number of osteons per unit area. From birth to adulthood, the thickness of the compact substance increases by 3-4 times, the content of mineral salts in it increases by 5 times, the maximum load increases by 3-4 times, reaching 280 in sheep and 1000 kg per 1 cm2 in cows. The bones of cattle reach their final strength by 12 months of age.

The larger the animal, the less strength it has in its bones. Males have thicker bones than females, but underfeeding affects them more strongly. Improved breeds of sheep and pigs have shorter and wider limb bones. Early maturing animals have thicker bones than late maturing animals. The bones of dairy cows are better supplied with blood, and in beef and meat-dairy cows the area of ​​the compact bone substance and the wall thickness are larger, which determines its greater strength under load. The bending strength of bone is determined by the structure of osteons. Landrace pigs, for example, have higher bone flexural strength than Large White and Northern Siberian breeds due to the fact that Landrace pigs have a denser arrangement of osteons.

Of all the external conditions, feeding and exercise have the greatest influence on the development of the skeleton. Improving feeding during the period intensive growth accelerates bone growth, underfeeding inhibits their growth rate, especially in width, but does not interfere general patterns skeletal growth. In pasture-raised animals, the compact bone substance is denser, lamellar structures predominate in it, the trabeculae of the spongy substance are thicker, more uniform in width and directed strictly according to the action of compression-tension forces. When keeping animals in stalls and cages, the growth and internal restructuring of bones slows down, their density and strength decreases compared to walking, floor keeping and animals subjected to dosed forced movement.

Adding macro- and microelements to the diet of young animals promotes the formation of bones with thicker compact substance and trabeculae and a smaller bone cavity. With a lack of minerals, demineralization of the skeleton occurs, softening and resorption of the vertebrae, starting with the caudal ones.

Spatula(Fig. 114, C) is wider at the base than in horses, due to a significant increase in the post-spinous fossa (5). The scapular spine is strongly developed, becomes higher towards the articular angle, but before reaching the last one, it breaks off abruptly; the top of this cliff represents the acromion (f); In ruminants, it becomes a lever of movement, projecting into the lateral side of the scapula, and serves as the attachment site for the acromial part of the deltoid muscle. The scapular cartilage generally resembles that of horses (3).
The shoulder blade of cattle is located at the articular angle at the level of the middle of the 2nd rib, the cervical angle - like that of a horse, and the dorsal angle - at the level of the vertebral ends of the 6-7th rib.
The humerus (Fig. 121-D) is shorter, but thicker than that of a horse. The head of the proximal end is distinctly separated from the body by the neck. The lateral muscular tubercle, together with the trochlear process, corresponds to the greater tubercle (a) and is strongly developed, so that the trochlear process even hangs over the intertubercular groove itself. The latter is not double, like horses, but single (6); The biceps brachii muscle is thrown across it. The medial muscular tubercle with its process is much smaller than the lateral one and corresponds to the lesser tubercle.

The deltoid roughness (d") does not protrude sharply. The block (g) of the distal end is located obliquely in such a way that its medial edge is lowered somewhat lower (distal). Otherwise, with slight deviations, the bone is close in structure to that of horses.
Sheep and goats have a more rounded humerus than cattle.
Bones of the forearm(radial and ulnar) (Fig. 117-D) are connected to each other by synostosis; between them there were only two narrow interosseous spaces - proximal (large) and distal (small). The vascular groove runs along the lateral side of the bone border.
The radius (1) is slightly curved, the roughness for the biceps muscle (c) is less clearly defined than in horses. The groove of the distal end is set obliquely (d). The grooves for the extensor tendons on the zinc surface at this end are barely noticeable.
The ulna (2) extends the entire length of the forearm and at the distal end even descends below the radius called the slate process (g). It has an articular facet for articulation with. carpal ulna. The olecranon process (h) is massive and slightly bifurcated.
In small ruminants, the structure of the forearm bones is generally the same, only the ulna in the middle section is somewhat more reduced, especially in goats.
Wrist(Fig. 122) consists of three bones in the proximal row, in addition to the accessory, and two brushes in the distal row. In the latter, the 1st carpal is missing, and the 2nd and 3rd merge into one bone (9).

In the proximal row, the carpal radius (8) has both surfaces strongly concave, especially towards the connection with the forearm. The carpal intermediate bone (7) is equipped with tortuous surfaces. The carpal ulna (4) has a proximal surface in the form of a sloping groove, and a process protrudes from the bone volarly, hanging down. The accessory bone (5) is rounded, with a thickened end and bears only one articular surface for articulation with the carpal ulna.
In the distal row, the fused carpal bones 2 and 3 (9) have a slightly convex proximal surface and a flat distal surface. It is approximately quadrangular and strongly flattened. The carpal 4+5 bone (6) is quite significant in size, and its height is greater than that of the neighboring one; the proximal surface is convex and descends volarly, and the distal surface is flat. The entire distal row of bones articulates only with the fused 3rd and 4th metacarpals.
There are three metacarpus bones (Fig. 122). Two of them, namely the 3rd and 4th metacarpal bones, are fused together into one bone (11) and are the main bones of the metacarpus; 1 and 2 are completely absent, although the embryo has its own anlage, which is reduced. The metacarpal 5th bone exists in the form of a small cone-shaped rudiment (10) with a blunt apex directed downward. It lies on the lateral side of the metacarpus and articulates with the 4th metacarpal at its proximal end.
Thus, only the fused 3rd and 4th bones can be described (11). They are equally massive. The process of their fusion, even from the outside, is clearly indicated by the sagittal groove (along which the vessel passes) on the dorsal side of the bone. A transverse cut of the bone reveals that a wall runs inside along this groove, dividing the metacarpus into two tubes.. Along this groove, there is an opening in the proximal and distal thirds; they continue into canals through the entire thickness of the bone onto its volar surface. The fusion of two bones into one is especially prominent at the distal end of the bone, where the fusion process ends for some distance; both bones here have their own independent ends with roller-shaped articular surfaces. On each ridge there is a raised ridge that divides the articular surface almost in half, with the lateral half of the ridge having a smaller radius than the one that lies towards the inter-roller notch. This complex bone, which has become a single bone, as indicated in the general part, is called the bone of the runners. At its proximal end there are flat articular surfaces for connection with the carpal bones, and on the dorsal surface there is a roughness visible for attachment of the extensor carpi radialis.
Finger bones(Fig. 122). In cattle, only two middle fingers exist, fully developed and functioning, namely the 3rd and 4th, corresponding to the ends of the main metacarpal bone. Each of these main fingers contains all three phalanges.
The first phalanx (14) of each finger is thickened at the ends, especially at the proximal one. The latter bears a concave articular surface with a groove almost in the middle. The ligamentous tuberosities, as well as small articular facets for the sesamoid bones, strongly protrude volarly. The body of the phalanx is approximately triangular, with a flat volar surface. The sides of the phalanges of both fingers, facing each other in the skeleton, are also flattened, and the lateral sides of both phalanges are convex and form a rounded edge on the dorsal side. The roll-shaped distal end is divided into two parts by a sagittal depression, of which the lateral one is slightly smaller than the neighboring one.
The second phalanx (15) of the fingers is shorter than the first and in general structure has the same features, but its proximal end bears an articular surface with a ridge. The ligamentous tuberosities are directed backwards. The body is even more triangular, since the edge of the dorsal surface protrudes more strongly. Distal end similar to that of the first phalanges, with the only difference that the articular platform extends somewhat further onto the dorsal surface. On the sides there are ligamentous fossae, of which those directed towards the middle (interdigital fissures) are deeper.
The third phalanx of the 3rd and 4th fingers (16), or the claw bone, has approximately the shape of a triangular pyramid with the apex directed forward. A rounded edge runs down the back surface, on both sides of which there are wall surfaces. Of these, the one facing the interdigital fissure is somewhat concave and set steeply, and the lateral one is convex and sloping. The articular (proximal) end has a bifid concave articular surface; the edge framing it towards the dorsal side is extended into the extensor (coronoid) process to secure the common digital extensor tendon. The volar articular surface is supplemented with facets for articulation with the sesamoid bones; There is also a protrusion here - the flexor process for attaching the deep digital flexor. The relatively wide supporting plantar surface has the shape of a crescent.
At the point where the plantar surface meets the wall there is a plantar edge, along which a vascular groove stretches on the lateral side, leading through the hole into the bone.
Foramina are also visible near the extensor process.
The pendulous fingers are highly vestigial and have two small phalanges (usually the 2nd and 3rd).
Sesamoid bones. On the volar surface of the joint of the 1st phalanx of the supporting fingers there are two sesamoid bones (Fig. 122-13). On the same surface of the joint of the 3rd phalanx there is one navicular bone (18).

The bones of the forearm - ossa antebrachii - are represented by two tubular bones; of these, the radial one lies dorsomedially, and the ulnar one lies laterovolar (). Both bones are well developed only in dogs and pigs. In a dog they are connected movably, but in a pig they are motionless. In cattle and horses, both bones are fused.

The radius, or simply ray, - radius - is characterized by:

• a) concave articular surface on the proximal epiphysis;
• b) massive distal epiphysis, bearing the articular surface, divided into 2-3 sections;
• c) facets or a rough surface for connection with the ulna or the presence of the latter (in a reduced form).

The proximal epiphysis is called radial head- capitulum radii; it bears a grooved articular surface - the fossa of the head - fossa capituli radii - for the block of the humerus. The fossa of the head in ungulates is divided into three parts by a groove and a comb. On the dorsal surface of the epiphysis there is a roughness of the radius - tuberositas bicipitalis radii - for attachment of the biceps brachii muscle, and on the lateral surface - ligamentous tubercle- tuberculum laterale.

On the distal epiphysis there is a concave or flat-concave articular surface - facies articularis - for articulation with the bones of the wrist.

Diaphysis, or body, radius slightly curved dorsally; its dorsal surface is smooth and passes into the lateral ones without noticeable boundaries; the volar surface is somewhat concave and more rough.

The ulna - ulna - in cases where it is well developed, is a tubular bone, longer than the radius. The big one stands out on her olecranon- olecranon, ending ulnar tubercle- tuber olecrani - for attaching powerful extensors of the elbow joint. The ulna forms to accommodate the block of the humerus semilunar notch- incisure semilunaris, s. trochlearis, limited dorsally uncinate process- processus anconaeus. The olecranon process is convex on the lateral surface and concave on the medial surface. The distal epiphysis is equipped with facets for connection with the carpal bones.

Peculiarities.
In a dog, both bones of the forearm are connected movably. The radius is long, thin, and dorsally curved. The fossa of the radial head is oval; on the mediovolar surface of the head a transverse, narrow, long facet for ulna- circumferentia articularis. A small facet for the same bone is also present on the distal epiphysis of the radius on its lateral surface. The articular surface for the carpal bones is a transverse oval fossa.

The ulnar tubercle bears two small tubercles. Below the semilunar notch there is a notch - incisura radialis - with a narrow facet - circumferentia articularis - for the head of the radius. The body of the ulna tapers distally. Its distal epiphysis is somewhat thickened, equipped medial facet for the radius and ends with the slate process.

The pig's forearm bones are short and massive. The ulna is connected by a wide, rough surface to the radius, and in adult animals these bones are fused. The body of the ulna is almost triangular-prismatic. On the articular surface of the dietal end of the radius, oblique ridges are visible.

In cattle, the radius bone is very highly developed; the more poorly developed ulna bone grows to it behind and laterally (but not along its entire length). Between both bones there remain two interosseous spaces - proximal and distal - spatium interosseum proximale et distale. On the lateral surface of the bones of the forearm, a vascular groove is noticeable - sulcus vascularis. The articular surface for the carpal bones is divided into three sections by oblique ridges. Ulnar tubercle with a small notch.

In a horse, the radius bone is highly developed. On the articular surface of its head there is a porcine fossa. Along the anterior edge of the articular surface of the distal epiphysis there is a clearly defined “splash” in the form of two pits, and at the back there is a ridge for articulation with the three carpal bones. On the dorsal surface of the epiphysis there are three grooves for muscle tendons. In the distal third of the volar surface of the diaphysis there is a roughness - tuberositas flexoria - for securing the tendon head of the superficial flexor of the digitorum.

The ulna is greatly reduced; only the proximal half remains, fused to the radius. The olecranon process and the semilunar notch are well defined. Between both bones of the forearm there remains an interosseous (proximal) space - spatium intero-sseum. Vessels and nerves pass through it. Distal to this space, both bones are fused, and proximally, they are connected by a joint and strong ligaments. The distal half of the ulna is sometimes found as a thin plate of bone.