![]() ![]() ![]() Darwin showed that in the course of evolution it was those kinds of movement and locomotor design that were vital and useful for the species that became fixed by natural selection. The movements in air of so-called flying fish, frogs, and mammals (for example, the flying squirrels) are not in fact flying but rather long, gliding jumps accomplished by means of such devices of support as elongated thoracic fins, interdigital membranes on the feet, and skin folds.Īs animals evolved, the kinds of movement changed and became more complex. Active movement in air-flying-is characteristic of most insects, birds, and some mammals (bats). Active movements in water are accomplished by specialized remigial structures (from hairs and flagella to the modified limbs of aquatic turtles, birds, and seals), by flexure of the entire body (most fish, caudate amphibians), and by jet action, ejecting water from body cavities (medusoids and cephalopods). Some aquatic animals have adaptations that maintain their bodies in a suspended state (for example, vacuoles in the external layer of protoplasm in radiolarians and air sacs in colonies of siphonophores). The soaring of birds, using air currents, is also a form of passive movement. For example, certain spiders release their silk and are borne through great distances by the air currents. ![]() Movements in water and air can also be passive. ![]() Purposeful movements are possible only through the coordinated work of a large number of muscles, which is effected by the nervous system. In all cases, the movements are the result of the interaction of forces external to the organism (gravity, environmental resistance) and internal forces (muscular tension, contraction of myofibrils, movements of protoplasm). Some aquatic animals, such as sponges and corals, which maintain a sedentary mode of life, use cilia and flagella to set their immediate environment in motion and bring them food.Īnimals can move about by (1) moving over a substrate, that is, upon solid or liquid support (walking, running, jumping, creeping, sliding), (2) moving freely in water (swimming), and (3) moving freely in air (flying). The most common construction of the locomotor organs, the limb, is a system of levers activated by muscular contractions. The organs may be pseudopodia (the slow flow from one place to another of protoplasm ameboid movement), cilia and flagella (ciliary and flagellar movement), or special body appendages by means of which the animals cling to a rough area of the substrate (setae, squamellae, scutella) or attach themselves to it (suckers). Movements are effected by specialized organs, the structure of which varies with the type of animal and depends on the type of locomotion and the nature of the habitat-terrestrial, aquatic, or aerial. Movements enable an organism to interact actively with the environment-specifically, to move from place to place and to capture food. The chin, mouth, nose, forehead and finally the occiput emerge.(in biology), one of the manifestations of vital activity.Īnimals and man. This set of movements is observed as external rotation of the shoulder, with the fetal back facing upwards. However, if the chin becomes anterior, rotational dystocia will occur. Totally flexed, the head goes through an internal rotation motion to place the occiput under the symphysis. The anterior shoulder is wedged under the symphysis pubis at the level of the acromion, while the posterior shoulder pushes the coccyx backwards and is expelled, followed by expulsion of the anterior shoulder. The biacromial diameter then becomes anteroposterior, the fetal back points to the maternal right or left side, and the head begins to flex. The upper limbs are forced into flexion, shortening the biacromial diameter before assuming an oblique diameter. The abdomen and the most inferior portion of the fetal chest are expelled. In complete breech presentation, the lower limbs are usually expelled at the same time as the buttocks. The posterior buttock pushes the coccyx backwards, distends the perineum, and then becomes exteriorized, which fully releases the anterior buttock. The anterior buttock descends under the pubic bone and begins to open the vulvar orifice. In the anterior positions, a 45-degree backward rotation in the posterior positions, a 45-degree forward rotation occurs. The bitrochanteric diameter descends obliquely with slight posterior asynclitisim ( the posterior buttock descends ahead of the anterior buttock, the intergluteal cleft is closer to the pubis than to the sacrum).Įngagement usually occurs in an oblique position (left sacrum anterior, right sacrum anterior, left sacrum posterior, right sacrum posterior).Ī 45-degree internal (ie, in the birth canal ) rotation occurs. ![]()
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