First Book in Physiology and Hygiene

by John Harvey Kellogg

CHAPTER XVIII.

OUR BONES AND THEIR USES.

1. The Bones.—In an earlier chapter we learned something about the bones. This we must try to recall. You will remember that we called the bones the framework of the body, just as the timbers which are first put up in building a house are called its frame.

2. The Skeleton.—All the bones together make up the skeleton. (See page 95.) There are about two hundred bones in all. They are of many different shapes. They vary in size from the little bones of the ear, which are the smallest, to the upper bone of the leg, which is the largest in the body.

3. The skeleton is divided into four parts: the skull, the trunk, the arms, and the legs. We must learn something more about the bones of each part.

4. The Skull.—The skull is somewhat like a shell. It is made of a number of bones joined together in such a way as to leave a hollow place inside to hold the brain. The front part of the skull forms the framework of the face and the jaws. In each ear there are three curious little bones, which aid us in hearing.

5. The Trunk.—The bones of the trunk are, the ribs, the breast-bone, the pelvis, and the back-bone. The bones of the trunk form a framework to support and protect the various organs within its cavities.

6. The Ribs.—There are twelve ribs on each side. The ribs join the back-bone at the back. They are connected by cartilage to the breast-bone in front. They look somewhat like the hoops of a barrel. With the breast-bone and the back-bone they form a bony cage to contain and protect the heart and the lungs.

7. The Pelvis.—The pelvis is at the lower part of the trunk. It is formed by three bones, closely joined together. The large bones at either side are called the hip-bones. Each hip-bone contains a deep round cavity in which the upper end of the thigh-bone rests.

8. The Back-bone.—The back-bone, or spinal column, is made up of twenty-four small bones, joined together in such a way that the whole can be bent in various directions. The skull rests upon the upper end of the spinal column. The lower end of the back-bone forms a part of the pelvis.

SKELETON OF A MAN.

9. The Spinal Canal.—Each of the separate bones that make up the back-bone has an opening through it, and the bones are so arranged, one above another, that the openings make a sort of canal in the back-bone. By the connection of the spinal column to the head, this canal opens into the cavity of the skull. Through this canal there passes a peculiar substance called the spinal cord, of which we shall learn more at another time.

10. The Arms.—Each of the arms has five bones, besides the small bones of the hand. They are the collar-bone, which connects the shoulder to the breast-bone, the shoulder-blade, at the back of the shoulders, the upper arm-bone, between the shoulder and the elbow, and the two lower arm-bones, between the elbow and the wrist. There are eight little bones in the wrist, five in that part of the hand next to the wrist, and fourteen in the fingers and thumb.

11. The Legs.—The bones of the leg are the thigh or upper leg-bone, the knee-pan or knee-cap, which covers the front of the knee, the two bones of the lower leg, the heel-bone and six other bones in the ankle, five bones in that part of the foot next to the ankle, and fourteen bones in the toes.

12. Use of the Bones.—The skeleton is not only necessary as a framework for the body, but it is useful in other ways. Some of the bones, as the skull, protect delicate parts. The brain is so soft and delicate that it would be very unsafe without its solid bony covering. The spinal cord also needs the protection which it finds in the strong but flexible back-bone. The bones help to move our hands and arms, and assist us in walking.

13. The Joints.—The places where two or more bones are fastened together are called joints. Some joints we can move very freely, as those of the shoulder and the hip. Others have no motion at all, as those of the bones of the skull.

14. Cartilage.—The ends of bones which come together to form a joint are covered with a smooth, tough substance, which protects the bone from wear. This is called gristle or cartilage. You have, no doubt, seen the gristle on the end of a "soup-bone" or on one of the bones of a "joint of beef."

15. The joint contains a fluid to oil it, so that the ends of the bones move upon each other very easily. If the joints were dry, every movement of the body would be very difficult and painful.

16. The bones are held together at the joints by means of strong bands called ligaments.

17. How the Bones are Made.—The bones are not so solid as they seem to be. The outside of most bones is much harder and firmer than the inside. Long bones, like those of the arms and the legs, are hollow. The hollow space is filled with marrow, in which are the blood-vessels which nourish the bone.

18. An Experiment.—If you will weigh a piece of bone, then burn it in the fire for several hours, and then weigh it again, you will find that it has lost about one third of its weight. You will also notice that it has become brittle, and that it seems like chalk.

19. Why the Bones are Brittle.—The hard, brittle portion of a bone which is left after it has been burned contains a good deal of chalk and other earthy substances, sometimes called bone-earth. It is this which makes the bones so hard and firm that they do not bend by the weight of the body. When we are young, the bones have less of this bone-earth, and so they bend easily, and readily get out of shape. When we get old, they contain so much bone-earth that they become more brittle, and often break very easily.

20. A person's height depends upon the length of his bones. The use of alcohol and tobacco by a growing boy has a tendency to stunt the growth of his bones, so that they do not develop as they should.

SUMMARY.

1.	There are about two hundred bones in the body.
2.	All together they are called the skeleton.
3.	The skeleton is divided as follows:
a.	The skull.
			{
					Ribs.
					Breast Bone.
b.	The Trunk.				Pelvis.
					Back Bone.
					Collar Bone.
					Shoulder Blade.
			{
					Upper arm-bones.
c.	The Arms.				Lower arm-bones.
					Wrist.
					Hand and fingers.
			{
					Thigh.
					Knee-pan.
d.	The legs.				Lower leg-bones.
					Ankle, including heel-bone.
					Foot and toes.

4. The bones are useful for support, protection, and motion.

5. The place where two bones join is called a joint.

6. The tough substance which covers the ends of many bones is called cartilage or gristle.

7. The joints are enabled to work easily by the aid of a fluid secreted for that purpose.

8. The ends of the bones are held together in a joint by means of ligaments.

9. Bones are about two thirds earthy matter and one third animal matter.

10. The use of alcohol and tobacco may prevent proper development of the bones.

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