Birds are animals that not only move on the earth, but also fly up in the air, soar in the sky. Therefore, as a result of evolutionary development, a change in the mass and shape of their body was observed. At the same time, there was an accumulation of fat - an energy reserve, friction decreased during movement, and muscle mass increased. At the same time, their skeleton and muscles changed, i.e. musculoskeletal system of birds.
In many ways, it is the same as that of mammals. The musculoskeletal system of birds consists of an axial skeleton, skull, humerus and forearm, scapula, thoracic vertebrae, pelvic and femoral bones, etc.
At the same time, it is completely different than the musculoskeletal system of mammals. For example, the bird’s head is small, because all the bones of the brain skull fused, and their number decreased. The skull is greatly relieved due to the fact that the bones are mostly hollow, and there is a toothless beak that is covered only with a horn cover. Birds do not have bends of the spine, as in humans. The chest "human" cell is expanded, and in animals and birds it is compressed laterally.
The cervical skeleton of birds is represented by 11-25 free vertebrae, but the thoracic vertebrae are firmly bonded to each other and along with the vertebrae of the lumbar region. The sacral region fused with the belt of the hind limbs, and the sacrum formed.
There is a difference in the facial skeleton, and in the belt of limbs, and in the limbs themselves. For example, only birds have a keel - a cartilaginous outgrowth that formed when the clavicle fused with the sternum. In flying birds, the sternum is quite developed, and the keel is large.
The musculoskeletal system of birds includes the hind limbs, which are two large, powerful pelvic bones fused with a complex sacrum. And since the bird walks on two legs, the sacrum itself is also powerful. The sacrum is formed by fused sacral, lumbar, and caudal vertebrae; therefore, it is believed that birds have no lumbar region.
The skeleton of a bird differs from the skeletons of other living beings in that it is strong and light. This is achieved, firstly, because the bones in birds are tubular. Secondly, lightness is explained by the bone cavity. Therefore, the mass of the skeleton of a bird is somewhere around 5 -15% of its body weight. With the exception of the cervical spine, the entire spine is motionless.
Since the forelimbs turned into wings as a result of evolutionary development, the hand is almost not developed. But in birds that fly well, large pectoral muscles make up somewhere between 15–20% of the mass, and their special location contributes to the stability of birds in the air.
Lower in development than birds and mammals is the reptile class. The body of such a reptile consists of a head, neck, trunk and limbs, except for snakes and legless lizards, which are deprived of limbs. By structure, the musculoskeletal system of reptiles is close to amphibians, but unlike them, it has a more ossified skeleton. A more progressive structure of the bone skeleton and muscles of such animals determined their mobility. The skeleton of reptiles, like the musculoskeletal system of birds, also consists of the cervical, thoracic, sacral and caudal sections. Long ribs connect to the sternum and a rib cage forms.
Reptiles, unlike other animals, have more dissected muscles, in particular, intercostal muscles. They can regulate the volume of the chest, compress and expand it, thereby making the process of breathing. Since the ribs of reptiles end freely, this allows them to swallow rather large food. Their tail section is well developed.
Summing up, it can be noted that the skeletons of all animals have distinctive features, but perform similar functions. They serve as the support of the body, protect internal organs and help to move all living things in space.