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.