~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. [Illustration: 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.