The Skeleton : Part 4

Physiology and Hygiene for Secondary Schools
by Francis M. Walters

(Page 17 of 28)

Kinds of Movable Joints. - The different kinds of movable joints are the ball and socket joint, the hinge joint, the pivot joint, the condyloid joint, and the gliding joint. These are constructed and admit of motion, as follows:

1. In the ball and socket joint the ball-shaped end of one bone fits into a cup-shaped cavity in another bone, called the socket. The best examples of such joints are found at the hips and shoulders. The ball and socket joint admits of motion in all directions.

2. In the hinge joint the bones are grooved and fit together after the manner of a hinge. Hinge joints are found at the elbows and knees and also in the fingers. The hinge joint gives motion in but two directions - forward and backward.

3. A pivot joint is formed by the fitting of a pivot-like projection of one bone into a ring-like receptacle of a second bone, so that one, or the other, is free to turn. A good example of the pivot joint is found at the elbow, where the radius turns upon the humerus. Another example is the articulation of the atlas with the axis vertebra as already noted. The pivot joint admits of motion around an axis.

4. The condyloid joint is formed by the fitting of the ovoid (egg-shaped) end of one bone into an elliptical cavity of a second bone. Examples of condyloid joints are found at the knuckles and where the wrist bones articulate with the radius and ulna. They move easily in two directions, like hinge joints, and slightly in other directions.

5. Gliding joints are formed by the articulation of plain (almost flat) surfaces. Examples of gliding joints are found in the articulations between the bones of the wrist and those of the ankle. They are the simplest of the movable joints and are formed by one bone gliding, or slipping, upon the surface of another.

The Machinery of the Body. - A machine is a contrivance for directing energy in doing work. A sewing machine, for example, so directs the energy of the foot that it is made to sew. Through its construction the machine is able to produce just that form of motion needed for its work, and no other forms, so that energy is not wasted in the production of useless motion. The places in machines where parts rub or turn upon each other are called bearings, and extra precautions are taken in the construction and care of the bearings to prevent friction.

The body cannot properly be compared to any single machine, but must be looked upon as a complex organization which employs a number of different kinds of machines in carrying on its work. The majority of these machines are found in the skeleton. The bones are the parts that are moved, and the joints serve as bearings. Connected with the bones are the muscles that supply energy, and attached to the muscles are the nerves that control the motion. Other parts also are required for rendering the machines of the body effective in doing work. These are supplied by the tissues connected with the bones and the muscles.

Hygiene of the Skeleton

Of chief concern in the hygiene of the skeleton is the proper adjustment of its parts. The efficiency of any of the body machines is impaired by lack of proper adjustment. Not only this, but because of the fact that the skeleton forms the groundwork of the whole body - muscles, blood vessels, nerves, everything in fact, being arranged with reference to it - any lack of proper adjustment of the bones interferes generally with the arrangement and work of tissues and organs. The displaced bones may even compress blood vessels and nerves and interfere, in this way, with the nourishment and control of organs remote from the places where the displacements occur. For these reasons the proper adjustment of the different parts of the skeleton supplies one of the essential conditions for preserving the health.

Hygienic Importance of the Spinal Column. - What has been said about the adjustment of the skeleton in general applies with particularly force to the spinal column. The spinal column serves both as the central axis of the body and as the container of the spinal cord. Thirty-one pairs of nerves pass between the vertebra to connect the spinal cord with different parts of the body, and two important arteries (the vertebral) pass through a series of small openings in the bones of the neck to reach the brain. Unnatural curves of the spine throw different parts of the body out of their natural positions, diminish the thoracic and abdominal cavities, and, according to the belief of certain physicians, compress the nerves that pass from the cord to other parts of the body. Slightly misplaced vertebra in the neck, by compressing the vertebral arteries, may also interfere with the supply of blood.

How the Skeleton becomes Deformed - We are accustomed to look upon the skeleton as a rigid framework which can get out of its natural form only through severe strain or by violence. This view is far from being correct. On account of their necessary freedom of motion, the bones, especially those of the spinal column, are easily slipped from their normal positions; and where improper attitudes are frequently assumed, or continued through long periods of time, the skeleton gradually becomes deformed For example, the habit of always sleeping on the same side with a high pillow may develop a bad crook in the neck; and the ugly curves, assumed so frequently in writing, and also in standing, when the weight is shifted too much on one foot, may become permanent. Then the habit of reclining in a chair with the hips resting on the front of the seat often deforms the back and causes a drooping of the shoulders. In fact, slight displacements of the vertebra come about so easily through incorrect positions, that they may almost be said to "occur of themselves" where active measures are not taken to preserve the natural form of the body. The very few people who have perfectly formed bodies show to what an extent has been overlooked an essential law of hygiene.

Prevention of Skeletal Deformities. - Those deformities of the skeleton that are acquired through improper positions are prevented by giving sufficient attention to the positions assumed in sitting, standing, and sleeping, and also to the posture in various kinds of work. In sitting the trunk should be erect and the hips should touch the back of the chair. One should not lounge in the ordinary chair. In standing the body should be erect, the shoulders back and down, the chest pushed slightly up and forward, and the chin slightly depressed, while the weight should, as a rule, rest about equally on the two feet. The habit of leaning against some object when standing (the pupil in reciting often leans on his desk) should be avoided. In sleeping the pillow should be of the right thickness to support the head on a level with the spinal column and should not be too soft. If one sleeps on his back, no pillow is required. It is best not to acquire the habit of sleeping always on the same side.

D.C. Heath and Co. - Publishers
Original copyright 1909