5. Tell about your foot.
Some joints, as those of the skull, are immovable; some, as those of the spine, may be moved a little; and others more or less freely, as those of the limbs. In machines, the parts which move upon each other need to be oiled, to keep them from wearing out; but the joints of our bodies oil themselves with a thin fluid, called synovia. This fluid resembles the white of an egg, and comes from a smooth lining inside of the joints. The ends of the bones which form joints are covered by gristle or cartilage, and are fastened together by very strong, silvery white bands, called ligaments. A sprain is caused by overstretching or tearing some of these ligaments.
QUESTIONS ON THE LIMBS AND JOINTS OF THE BODY.
What is the trunk of your body?—"All the body but the head and limbs."
Which are your limbs?—"My two arms and my two legs."